.hero {
  display: grid;
  grid-template-columns: minmax(0, 0.9fr) minmax(520px, 1.1fr);
  align-items: center;
  gap: clamp(2rem, 5vw, 5rem);
  min-height: 700px;
  padding-top: clamp(4rem, 7vw, 7rem);
  padding-bottom: clamp(5rem, 8vw, 8rem);
  background:
    radial-gradient(circle at 80% 28%, rgba(20, 184, 166, 0.09), transparent 25rem),
    radial-gradient(circle at 5% 80%, rgba(98, 230, 210, 0.06), transparent 24rem);
}

/* Teaching views: explanation / code / demo */
.lesson-mode-tabs {
  display: inline-flex !important;
  align-items: center !important;
  gap: 0.2rem !important;
  padding: 0.25rem;
  border: 1px solid #e3e7f2;
  border-radius: 12px;
  background: #f5f7fb;
}

.lesson-mode-tabs[hidden] { display: none !important; }

.lesson-mode-tabs button {
  min-height: 30px;
  padding: 0 0.8rem;
  border: 0;
  border-radius: 8px;
  color: #7b8497;
  background: transparent;
  font-size: 0.64rem;
  font-weight: 760;
}

.lesson-mode-tabs button:hover {
  color: var(--color-primary);
  background: rgba(255, 255, 255, 0.75);
}

.lesson-mode-tabs button.active {
  color: #fff;
  background: var(--gradient-brand);
  box-shadow: 0 6px 14px rgba(15, 143, 131, 0.2);
}

.study-panel[hidden] { display: none !important; }

.study-panel.active {
  animation: panel-enter 220ms var(--ease) both;
}

@keyframes panel-enter {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

.theory-grid,
.axis-theory,
.code-lesson-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(300px, 0.95fr);
  gap: 1rem;
  align-items: stretch;
}

.reading-card {
  padding: clamp(1.35rem, 2.5vw, 2.2rem);
  border: 1px solid var(--color-line);
  border-radius: 22px;
  background: #fff;
  box-shadow: var(--shadow-sm);
}

.reading-card-primary {
  background:
    radial-gradient(circle at 100% 0%, rgba(20, 184, 166, 0.1), transparent 14rem),
    #fff;
}

.reading-kicker,
.code-explanation > span {
  color: var(--color-primary);
  font-size: 0.6rem;
  font-weight: 850;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.reading-card h3,
.code-explanation h3 {
  margin: 0.7rem 0 1rem;
  font-size: clamp(1.25rem, 2vw, 1.75rem);
  line-height: 1.25;
  letter-spacing: -0.03em;
}

.reading-card > p {
  margin: 0.7rem 0 0;
  color: #596276;
  font-size: 0.78rem;
  line-height: 1.85;
}

.reading-card strong { color: var(--color-text); }

.key-callout {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 0.75rem;
  margin-top: 1.25rem;
  padding: 0.85rem 1rem;
  border: 1px solid rgba(15, 143, 131, 0.12);
  border-radius: 14px;
  color: #4f5b75;
  background: var(--color-blue-soft);
  font-size: 0.69rem;
  line-height: 1.65;
}

.key-callout b { color: var(--color-primary); white-space: nowrap; }
.key-callout.warning { border-color: rgba(255, 159, 67, 0.18); background: #fff8ed; }
.key-callout.warning b { color: #b86a12; }

.lesson-notes {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
  margin-top: 0.85rem;
}

.lesson-notes article {
  padding: 1rem 1.1rem;
  border: 1px solid var(--color-line);
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.82);
}

.lesson-notes article::before {
  display: inline-block;
  margin-right: 0.45rem;
  color: #38a36f;
  content: "✓";
}

.lesson-notes article.pitfall::before { color: #e48531; content: "!"; }
.lesson-notes b { font-size: 0.72rem; }
.lesson-notes p { margin: 0.5rem 0 0; color: var(--color-muted); font-size: 0.67rem; line-height: 1.65; }
.compact-notes { margin-top: 1rem; }

.lesson-code-card {
  min-width: 0;
  overflow: hidden;
  border: 1px solid #29314f;
  border-radius: 20px;
  color: #eaf9f6;
  background: #12182c;
  box-shadow: 0 18px 38px rgba(21, 29, 56, 0.16);
}

.lesson-code-card > header {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 0.8rem;
  min-height: 46px;
  padding: 0 1rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
  background: rgba(255, 255, 255, 0.035);
}

.lesson-code-card > header > div { display: flex; gap: 0.3rem; }
.lesson-code-card > header i { width: 7px; height: 7px; border-radius: 50%; background: #ff6b66; }
.lesson-code-card > header i:nth-child(2) { background: #ffc85a; }
.lesson-code-card > header i:nth-child(3) { background: #4bd38a; }
.lesson-code-card > header span { color: #8f9abc; font: 0.6rem/1 ui-monospace, SFMono-Regular, Menlo, monospace; }

.lesson-code-card button,
.lesson-code-card .copy-tree {
  min-height: 28px;
  padding: 0 0.65rem;
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 7px;
  color: #bfc7e2;
  background: rgba(255, 255, 255, 0.06);
  font-size: 0.58rem;
  cursor: pointer;
}

.lesson-code-card button:hover { color: #fff; background: rgba(255, 255, 255, 0.12); }

.lesson-code-card pre {
  min-height: 300px;
  margin: 0;
  padding: 1.25rem;
  overflow: auto;
  color: #d9f5ef;
  font: 0.7rem/1.78 ui-monospace, SFMono-Regular, Menlo, monospace;
  tab-size: 2;
  white-space: pre-wrap;
}

.lesson-code-card .code-card-bar + pre { min-height: 300px; }
.code-comment { color: #7f8aad; }

.code-explanation {
  padding: clamp(1.3rem, 2.5vw, 2rem);
  border: 1px solid var(--color-line);
  border-radius: 20px;
  background: #fff;
}

.code-explanation ol { display: grid; gap: 0.6rem; margin: 0; padding: 0; list-style: none; counter-reset: code-step; }
.code-explanation li { position: relative; padding: 0.8rem 0.9rem 0.8rem 2.7rem; border-radius: 13px; background: #f7f8fb; counter-increment: code-step; }
.code-explanation li::before { position: absolute; top: 0.72rem; left: 0.85rem; display: grid; width: 22px; height: 22px; place-items: center; border-radius: 7px; color: #fff; background: var(--gradient-brand); content: counter(code-step); font-size: 0.56rem; font-weight: 800; }
.code-explanation li b { font-size: 0.71rem; }
.code-explanation li p { margin: 0.25rem 0 0; color: var(--color-muted); font-size: 0.65rem; line-height: 1.55; }

.demo-instruction {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.8rem;
  padding: 0.7rem 0.9rem;
  border: 1px solid rgba(15, 143, 131, 0.12);
  border-radius: 13px;
  background: var(--color-blue-soft);
}

.demo-instruction span { flex: 0 0 auto; color: var(--color-primary); font-size: 0.6rem; font-weight: 850; letter-spacing: 0.08em; }
.demo-instruction p { margin: 0; color: #5f6980; font-size: 0.68rem; line-height: 1.5; }

.layout-guide-grid {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 0.65rem;
}

.layout-guide-grid article {
  min-height: 190px;
  padding: 1.15rem;
  border: 1px solid var(--color-line);
  border-radius: 18px;
  background: #fff;
  transition: transform 180ms var(--ease), box-shadow 180ms ease;
}

.layout-guide-grid article:hover { transform: translateY(-3px); box-shadow: var(--shadow-md); }
.layout-guide-grid span { color: var(--color-primary); font-size: 0.58rem; font-weight: 850; }
.layout-guide-grid h3 { margin: 1rem 0 0.55rem; font-size: 1.05rem; }
.layout-guide-grid p { margin: 0; color: #596276; font-size: 0.68rem; line-height: 1.65; }
.layout-guide-grid small { display: block; margin-top: 0.8rem; color: #8c94a5; font-size: 0.59rem; line-height: 1.5; }

.decision-strip {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.8rem;
  margin-top: 0.8rem;
  padding: 0.9rem;
  border-radius: 15px;
  color: #667085;
  background: #f1f4fb;
  font-size: 0.66rem;
}

.decision-strip b { color: var(--color-text); }
.decision-strip i { width: 18px; height: 1px; background: #c8cfde; }

.method-code-columns {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.8rem;
}

.mini-code-card {
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: 19px;
  background: #fff;
  box-shadow: var(--shadow-sm);
}

.mini-code-card > span { display: block; padding: 1rem 1rem 0; color: var(--color-primary); font-size: 0.58rem; font-weight: 850; letter-spacing: 0.08em; }
.mini-code-card pre { min-height: 150px; margin: 0.8rem 0; padding: 1rem; overflow: auto; color: #d9f5ef; background: #151b30; font: 0.66rem/1.7 ui-monospace, SFMono-Regular, Menlo, monospace; white-space: pre-wrap; }
.mini-code-card p { margin: 0; padding: 0 1rem 1rem; color: var(--color-muted); font-size: 0.65rem; line-height: 1.55; }
.mini-code-card.featured { border-color: rgba(15, 143, 131, 0.2); box-shadow: 0 12px 28px rgba(15, 143, 131, 0.1); }

.method-demo,
.semantic-inspector,
.principle-demo {
  padding: 1rem;
  border: 1px solid var(--color-line);
  border-radius: 20px;
  background: #fff;
  box-shadow: var(--shadow-sm);
}

.method-demo-controls,
.semantic-buttons,
.principle-demo-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 0.8rem;
}

.method-demo-controls button,
.semantic-buttons button,
.principle-demo-controls button {
  min-height: 34px;
  padding: 0 0.85rem;
  border: 1px solid #e2e6f0;
  border-radius: 9px;
  color: #697287;
  background: #f7f8fb;
  font-size: 0.65rem;
  cursor: pointer;
}

.method-demo-controls button.active,
.semantic-buttons button.active,
.principle-demo-controls button.active {
  border-color: transparent;
  color: #fff;
  background: var(--gradient-brand);
}

.method-demo-stage {
  display: block;
  min-height: 230px;
  padding: 1rem;
  border: 1px dashed #ccd3e2;
  border-radius: 15px;
  background: #f8f9fc;
  transition: all 220ms var(--ease);
}

.method-demo-stage i { display: grid; width: 80px; height: 54px; margin-bottom: 0.6rem; place-items: center; border-radius: 13px; color: #fff; background: var(--gradient-brand); font-style: normal; font-weight: 800; }
.method-demo-stage.mode-flex { display: flex; align-items: center; justify-content: space-between; }
.method-demo-stage.mode-flex i { margin: 0; }
.method-demo-stage.mode-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 0.75rem; }
.method-demo-stage.mode-grid i { width: 100%; height: 90px; margin: 0; }

.method-demo-result,
.semantic-result {
  display: grid;
  grid-template-columns: auto auto 1fr;
  align-items: center;
  gap: 0.7rem;
  margin-top: 0.8rem;
  padding: 0.8rem 0.9rem;
  border-radius: 13px;
  background: #f2f4f9;
}

.method-demo-result span,
.semantic-result small { color: #8a92a5; font-size: 0.56rem; font-weight: 800; }
.method-demo-result code,
.semantic-result strong { color: var(--color-primary); font-size: 0.68rem; }
.method-demo-result p,
.semantic-result p { margin: 0; color: #687185; font-size: 0.64rem; line-height: 1.5; }

.axis-map,
.grid-vocabulary,
.breakpoint-list {
  display: grid;
  gap: 0.7rem;
}

.axis-map div,
.grid-vocabulary div,
.breakpoint-list article {
  display: grid;
  align-content: center;
  padding: 1.2rem;
  border: 1px solid var(--color-line);
  border-radius: 18px;
  background: #fff;
}

.axis-map span,
.breakpoint-list span { color: var(--color-primary); font-size: 0.58rem; font-weight: 850; letter-spacing: 0.08em; }
.axis-map b,
.breakpoint-list b { margin-top: 0.4rem; font-size: 0.9rem; }
.axis-map p,
.breakpoint-list p { margin: 0.35rem 0 0; color: var(--color-muted); font-size: 0.64rem; line-height: 1.55; }
.grid-vocabulary { grid-template-columns: repeat(2, 1fr); }
.grid-vocabulary div { min-height: 105px; }
.grid-vocabulary b { color: var(--color-primary); font: 800 0.8rem/1 ui-monospace, SFMono-Regular, Menlo, monospace; }
.grid-vocabulary span { margin-top: 0.45rem; color: var(--color-muted); font-size: 0.64rem; line-height: 1.5; }

.semantic-inspector {
  display: grid;
  grid-template-columns: 130px minmax(0, 1fr) 220px;
  gap: 1rem;
  align-items: stretch;
}

.semantic-buttons { align-content: start; margin: 0; }
.semantic-buttons button { width: 100%; text-align: left; }
.semantic-canvas { display: grid; grid-template-rows: 58px 44px minmax(160px, 1fr) 48px; gap: 7px; padding: 0.75rem; border-radius: 15px; background: #f1f3f8; }
.semantic-canvas [data-semantic-region] { display: grid; place-items: center; border: 1px solid #d8deeb; border-radius: 10px; color: #8a93a7; background: #fff; transition: all 180ms var(--ease); }
.semantic-canvas [data-semantic-region].active { border-color: rgba(15, 143, 131, 0.36); color: #fff; background: var(--gradient-brand); box-shadow: 0 8px 18px rgba(15, 143, 131, 0.18); transform: scale(1.015); }
.semantic-middle { display: grid; grid-template-columns: 1fr 32%; gap: 7px; }
.semantic-result { grid-template-columns: 1fr; align-content: center; margin: 0; }
.semantic-result strong { font-size: 1rem; }

.principle-stage {
  display: grid;
  grid-template-columns: 1.25fr 0.75fr;
  gap: 1rem;
  min-height: 260px;
  padding: 1.2rem;
  border: 1px dashed #cbd2e1;
  border-radius: 16px;
  background: #f6f7fa;
}

.principle-stage article { padding: 1.5rem; border: 1px solid #e0e4ed; border-radius: 18px; background: #fff; transition: all 260ms var(--ease); }
.principle-stage small { color: var(--color-primary); font-size: 0.56rem; font-weight: 850; letter-spacing: 0.1em; }
.principle-stage h3 { margin: 0.7rem 0; font-size: 1.15rem; }
.principle-stage p { color: var(--color-muted); font-size: 0.68rem; line-height: 1.6; }
.principle-stage button { min-height: 36px; padding: 0 0.9rem; border: 0; border-radius: 9px; color: #fff; background: var(--gradient-brand); font-size: 0.64rem; }
.principle-stage.is-before { grid-template-columns: 1fr 1fr; gap: 0.25rem 1.8rem; }
.principle-stage.is-before article:first-child { padding: 0.7rem 2.2rem 2.4rem 0.5rem; border-radius: 4px 22px 8px 3px; transform: translateY(13px); }
.principle-stage.is-before article:last-child { padding: 2rem 0.5rem 0.6rem 1.8rem; border-radius: 28px 3px 18px 7px; transform: translateY(-7px); }
.principle-stage.is-before h3 { font-size: 0.9rem; font-weight: 500; }
.principle-stage.is-before p { color: #858a95; }
.principle-demo > p { margin: 0.8rem 0 0; color: #687185; font-size: 0.67rem; line-height: 1.55; }
.principle-demo > p b { color: var(--color-text); }

@media (max-width: 1050px) {
  .layout-guide-grid { grid-template-columns: repeat(3, 1fr); }
  .theory-grid,
  .axis-theory,
  .code-lesson-grid { grid-template-columns: 1fr; }
  .semantic-inspector { grid-template-columns: 110px minmax(0, 1fr); }
  .semantic-result { grid-column: 1 / -1; grid-template-columns: auto auto 1fr; }
}

@media (max-width: 760px) {
  .lesson-toolbar-title strong { max-width: 150px; }
  .lesson-notes,
  .method-code-columns { grid-template-columns: 1fr; }
  .layout-guide-grid { grid-template-columns: repeat(2, 1fr); }
  .decision-strip { align-items: flex-start; flex-direction: column; }
  .decision-strip i { display: none; }
  .principle-stage { grid-template-columns: 1fr; }
}

@media (max-width: 560px) {
  .lesson-toolbar-title { display: none !important; }
  .lesson-toolbar { gap: 0.35rem; }
  .lesson-mode-tabs { display: inline-flex !important; margin-right: auto; }
  .lesson-mode-tabs[hidden] { display: none !important; }
  .lesson-mode-tabs button {
    display: inline-flex;
    width: auto;
    min-width: 50px;
    min-height: 30px;
    padding: 0 0.6rem;
    overflow: visible;
    color: #7b8497;
    font-size: 0.6rem;
  }
  .lesson-mode-tabs button.active { color: #fff; }
  .reading-card { padding: 1.15rem; }
  .layout-guide-grid { grid-template-columns: 1fr; }
  .layout-guide-grid article { min-height: auto; }
  .method-code-columns { grid-template-columns: 1fr; }
  .lesson-code-card pre { min-height: 0; font-size: 0.62rem; }
  .semantic-inspector { grid-template-columns: 1fr; }
  .semantic-buttons { display: flex; }
  .semantic-buttons button { width: auto; }
  .semantic-result { grid-column: auto; grid-template-columns: 1fr; }
  .principle-stage,
  .principle-stage.is-before { grid-template-columns: 1fr; }
  .grid-vocabulary { grid-template-columns: 1fr 1fr; }
}

.chapter-kicker {
  display: flex;
  align-items: center;
  gap: 0.7rem;
  margin-bottom: 1.65rem;
  color: var(--color-primary);
  font-size: 0.73rem;
  font-weight: 850;
  letter-spacing: 0.17em;
}

.chapter-kicker i {
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: #9da8c2;
}

.hero h1 {
  margin-bottom: 1.6rem;
  font-size: clamp(4rem, 6.2vw, 6.5rem);
  line-height: 0.94;
  letter-spacing: -0.075em;
}

.hero-copy > p {
  max-width: 560px;
  margin-bottom: 2rem;
  color: var(--color-muted);
  font-size: 1.04rem;
  line-height: 1.9;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-bottom: 2.4rem;
}

.hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 1.3rem;
  color: #8991a3;
  font-size: 0.73rem;
}

.hero-meta span {
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.hero-meta b {
  color: var(--color-ink);
  font-size: 0.86rem;
}

.hero-visual {
  position: relative;
  min-height: 520px;
}

.browser-card {
  position: absolute;
  z-index: 2;
  top: 48px;
  left: 6%;
  width: 88%;
  overflow: hidden;
  border: 1px solid rgba(151, 161, 190, 0.45);
  border-radius: 24px;
  background: #fff;
  box-shadow: 0 35px 70px rgba(15, 118, 110, 0.18), 18px 18px 0 rgba(15, 143, 131, 0.07);
  transform: rotate(1.4deg);
}

.browser-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 58px;
  padding: 0 1.1rem;
  border-bottom: 1px solid var(--color-line);
  background: #f9fafc;
  color: #9aa1b1;
  font: 0.68rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.browser-bar > span {
  min-width: 44%;
  padding: 0.55rem 1rem;
  border: 1px solid var(--color-line);
  border-radius: 999px;
  background: #fff;
  text-align: center;
}

.window-dots {
  display: flex;
  gap: 5px;
}

.window-dots i,
.code-card-bar > span i {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: #d5d8df;
}

.browser-more {
  letter-spacing: 0.15em;
}

.browser-layout {
  display: grid;
  grid-template-columns: 0.58fr 1.65fr 0.72fr;
  grid-template-rows: 68px 275px 58px;
  gap: 8px;
  padding: 12px;
  background: #f6f7fb;
}

.region {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  border: 1px solid rgba(15, 143, 131, 0.13);
  border-radius: 11px;
  color: #5e7f7a;
  background: #f0fdfa;
  font-size: 0.65rem;
  font-weight: 750;
  letter-spacing: 0.04em;
}

.region-header {
  grid-column: 1 / -1;
  justify-content: flex-start;
  gap: 0.45rem;
  padding: 0 1rem;
  color: var(--color-primary);
  background: #e3f8f4;
}

.region-header span {
  margin-right: auto;
}

.region-header i {
  width: 38px;
  height: 5px;
  border-radius: 999px;
  background: rgba(15, 143, 131, 0.22);
}

.region-sidebar,
.region-aside {
  align-items: flex-start;
  padding-top: 1rem;
  background: #f2f4fa;
  color: #858da3;
}

.region-main {
  flex-direction: column;
  align-items: stretch;
  justify-content: flex-start;
  padding: 1rem;
  background: #fff;
  color: var(--color-ink);
}

.content-lines {
  display: grid;
  gap: 7px;
  margin: 1rem 0 1.2rem;
}

.content-lines i {
  width: 90%;
  height: 6px;
  border-radius: 999px;
  background: #e6e9f1;
}

.content-lines i:nth-child(2) { width: 70%; }
.content-lines i:nth-child(3) { width: 82%; }

.content-cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 7px;
}

.content-cards i {
  height: 98px;
  border-radius: 8px;
  background: linear-gradient(145deg, #d9f5ef, #f0fdfa);
}

.region-footer {
  grid-column: 1 / -1;
  background: #ebeef5;
  color: #858da3;
}

.floating-card {
  position: absolute;
  z-index: 4;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  min-width: 165px;
  padding: 0.85rem 1rem;
  border: 1px solid rgba(215, 220, 231, 0.8);
  border-radius: 16px;
  background: rgba(255, 255, 255, 0.94);
  box-shadow: 0 15px 35px rgba(51, 61, 110, 0.14);
  backdrop-filter: blur(10px);
}

.floating-card > span:first-child {
  display: grid;
  width: 38px;
  height: 38px;
  place-items: center;
  border-radius: 11px;
  color: #fff;
  background: var(--gradient-brand);
  font-size: 0.74rem;
  font-weight: 800;
}

.floating-card div {
  display: grid;
  gap: 2px;
}

.floating-card strong { font-size: 0.75rem; }
.floating-card small { color: var(--color-muted); font-size: 0.62rem; }

.floating-code {
  top: 8px;
  right: -2%;
}

.floating-grid {
  right: 2%;
  bottom: 0;
}

.floating-card .mini-grid {
  display: grid !important;
  grid-template-columns: repeat(2, 7px);
  gap: 3px;
  align-content: center;
  justify-content: center;
}

.floating-card .mini-grid i {
  width: 7px;
  height: 7px;
  border-radius: 2px;
  background: #fff;
}

.orbit {
  position: absolute;
  border: 1px dashed rgba(15, 143, 131, 0.18);
  border-radius: 50%;
}

.orbit-one { inset: 0 1% 8% 6%; }
.orbit-two { inset: 12% 10% 0 0; }

.learning-strip {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: clamp(0.8rem, 2.4vw, 2.5rem);
  min-height: 84px;
  padding: 1rem 2rem;
  border-top: 1px solid var(--color-line);
  border-bottom: 1px solid var(--color-line);
  background: #fff;
  color: var(--color-muted);
  font-size: 0.75rem;
}

.learning-strip > span {
  color: var(--color-primary);
  font-weight: 850;
  letter-spacing: 0.16em;
}

.learning-strip div {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  white-space: nowrap;
}

.learning-strip i {
  display: grid;
  width: 28px;
  height: 28px;
  place-items: center;
  border-radius: 50%;
  color: var(--color-primary);
  background: var(--color-blue-soft);
  font-style: normal;
  font-size: 0.62rem;
  font-weight: 800;
}

.learning-strip b {
  color: #c0c6d5;
}

.concept-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 1.5rem;
}

.anatomy-card {
  padding: 1.25rem;
}

.case-step {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  align-items: center;
  gap: 1rem;
  margin: -0.65rem 0 1.35rem;
  padding: 0.75rem 0.9rem;
  border: 1px solid rgba(15, 143, 131, 0.13);
  border-radius: 15px;
  background: linear-gradient(110deg, rgba(238, 244, 255, 0.96), rgba(247, 244, 255, 0.82));
}

.case-step > span {
  padding: 0.45rem 0.62rem;
  border-radius: 9px;
  color: #fff;
  background: var(--gradient-brand);
  font-size: 0.56rem;
  font-weight: 850;
  letter-spacing: 0.08em;
  white-space: nowrap;
}

.case-step > div {
  display: flex;
  align-items: baseline;
  gap: 0.65rem;
  min-width: 0;
}

.case-step b {
  flex: 0 0 auto;
  color: #27345b;
  font-size: 0.7rem;
}

.case-step p {
  margin: 0;
  color: #667085;
  font-size: 0.68rem;
  line-height: 1.55;
}

.case-brief {
  display: grid;
  grid-template-columns: 1.15fr 0.9fr 0.9fr;
  gap: 0.8rem;
  margin-bottom: 1.2rem;
  padding: 1rem;
  border: 1px solid rgba(15, 143, 131, 0.13);
  border-radius: 20px;
  background: #fff;
  box-shadow: var(--shadow-sm);
}

.case-brief > div,
.case-brief article {
  padding: 0.95rem;
  border-radius: 14px;
  background: #f8f9fc;
}

.case-brief > div {
  color: #fff;
  background: var(--gradient-brand);
}

.case-brief span {
  display: block;
  margin-bottom: 0.6rem;
  color: rgba(255, 255, 255, 0.72);
  font-size: 0.56rem;
  font-weight: 850;
  letter-spacing: 0.12em;
}

.case-brief h3,
.case-brief p { margin: 0; }

.case-brief h3 {
  font-size: 1rem;
  line-height: 1.4;
}

.case-brief article b {
  color: var(--color-primary);
  font-size: 0.68rem;
}

.case-brief article p {
  margin-top: 0.55rem;
  color: #667085;
  font-size: 0.69rem;
  line-height: 1.65;
}

.theory-pair {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
  margin: 1rem 0;
}

.theory-pair > div {
  padding: 0.8rem;
  border: 1px solid rgba(15, 143, 131, 0.1);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.72);
}

.theory-pair b {
  color: var(--color-primary);
  font-size: 0.66rem;
}

.theory-pair p {
  margin: 0.4rem 0 0 !important;
  font-size: 0.65rem !important;
  line-height: 1.55 !important;
}

.journey-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin-bottom: 0.85rem;
}

.journey-controls button {
  min-height: 34px;
  padding: 0 0.8rem;
  border: 1px solid #e0e5f1;
  border-radius: 10px;
  color: #667085;
  background: #fff;
  font-size: 0.65rem;
  font-weight: 750;
  cursor: pointer;
  transition: border-color 180ms ease, color 180ms ease, background 180ms ease, transform 180ms ease;
}

.journey-controls button:hover {
  border-color: #afe7de;
  color: var(--color-primary);
  transform: translateY(-1px);
}

.journey-controls button.active {
  border-color: transparent;
  color: #fff;
  background: var(--gradient-brand);
}

.anatomy-diagram [data-journey-region] {
  opacity: 0.45;
  filter: saturate(0.65);
  transition: opacity 220ms ease, filter 220ms ease, transform 220ms ease, box-shadow 220ms ease;
}

.anatomy-diagram [data-journey-region].journey-active {
  z-index: 1;
  opacity: 1;
  filter: none;
  transform: scale(1.018);
  box-shadow: 0 9px 24px rgba(15, 143, 131, 0.17);
}

.journey-result {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  align-items: center;
  gap: 0.75rem;
  margin-top: 0.85rem;
  padding: 0.7rem 0.8rem;
  border-radius: 11px;
  background: #f5f7fc;
}

.journey-result small {
  color: var(--color-primary);
  font-size: 0.57rem;
  font-weight: 850;
  letter-spacing: 0.08em;
}

.journey-result p {
  margin: 0;
  color: #667085;
  font-size: 0.65rem;
  line-height: 1.55;
}

.theory-band {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.8rem;
  margin-bottom: 1rem;
}

.theory-band article {
  padding: 0.95rem 1rem;
  border: 1px solid rgba(15, 143, 131, 0.12);
  border-radius: 15px;
  background: linear-gradient(120deg, #f8faff, #faf8ff);
}

.theory-band b {
  color: var(--color-primary);
  font-size: 0.72rem;
}

.theory-band p {
  margin: 0.45rem 0 0;
  color: #667085;
  font-size: 0.68rem;
  line-height: 1.65;
}

.card-label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
  color: #81899d;
  font-size: 0.71rem;
  font-weight: 700;
  letter-spacing: 0.07em;
}

.card-label span,
.live-dot::before {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: #37c785;
  box-shadow: 0 0 0 4px rgba(55, 199, 133, 0.12);
}

.anatomy-diagram {
  display: grid;
  grid-template-rows: 82px 52px 245px 65px;
  gap: 8px;
  min-height: 470px;
  padding: 10px;
  border-radius: 17px;
  background: #f4f6fa;
}

.anatomy-diagram > div,
.anatomy-body > div {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  border: 1px solid rgba(15, 143, 131, 0.1);
  border-radius: 12px;
  color: #5f7f7a;
  background: #e3f8f4;
}

.anatomy-diagram b { font-size: 0.82rem; }
.anatomy-diagram small { color: #8993b0; font-size: 0.67rem; }
.anatomy-nav { background: #eefaf7 !important; }

.anatomy-body {
  display: grid;
  grid-template-columns: 2.1fr 0.9fr;
  gap: 8px;
}

.anatomy-main {
  color: #fff !important;
  background: var(--gradient-brand) !important;
  box-shadow: 0 12px 30px rgba(15, 143, 131, 0.2);
}

.anatomy-main small { color: rgba(255, 255, 255, 0.7) !important; }
.anatomy-side { background: #f3fbf9 !important; }
.anatomy-footer { color: #7e879b !important; background: #eceff5 !important; }

.region-list {
  display: grid;
  gap: 0.75rem;
}

.region-list article {
  display: flex;
  align-items: center;
  gap: 1rem;
  min-height: 82px;
  padding: 0.85rem 1.1rem;
  border: 1px solid var(--color-line);
  border-radius: 17px;
  background: rgba(255, 255, 255, 0.72);
  transition: border-color 180ms ease, transform 180ms var(--ease), box-shadow 180ms ease;
}

.region-list article:hover {
  border-color: rgba(15, 143, 131, 0.25);
  background: #fff;
  box-shadow: var(--shadow-sm);
  transform: translateX(5px);
}

.region-list article > span {
  display: grid;
  flex: 0 0 40px;
  height: 40px;
  place-items: center;
  border-radius: 12px;
  color: var(--color-primary);
  background: var(--color-blue-soft);
  font-size: 0.8rem;
  font-weight: 850;
}

.region-list h3 {
  margin-bottom: 0.22rem;
  font-size: 0.92rem;
}

.region-list p {
  margin: 0;
  color: var(--color-muted);
  font-size: 0.76rem;
  line-height: 1.6;
}

.structure-grid {
  display: grid;
  grid-template-columns: 0.9fr 1.1fr;
  align-items: stretch;
  gap: 1.5rem;
}

.code-card {
  overflow: hidden;
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: var(--radius-lg);
  color: #d9f5ef;
  background: #121521;
  box-shadow: 0 24px 55px rgba(20, 24, 42, 0.2);
}

.code-card-bar {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 1rem 1.1rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.07);
  color: #8f98ad;
  background: #191d2a;
}

.code-card-bar > span {
  display: flex;
  gap: 5px;
}

.code-card-bar > span i:nth-child(1) { background: #ff6b66; }
.code-card-bar > span i:nth-child(2) { background: #ffc85a; }
.code-card-bar > span i:nth-child(3) { background: #4bd38a; }

.code-card-bar small {
  font: 0.68rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.copy-tree {
  justify-self: end;
  padding: 0.3rem 0.55rem;
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 7px;
  color: #9fa9bd;
  background: transparent;
  font-size: 0.64rem;
  cursor: pointer;
}

.copy-tree:hover { color: #fff; background: rgba(255, 255, 255, 0.06); }

.code-card pre {
  margin: 0;
  padding: 2.1rem 2.4rem;
  font: 0.92rem/2.05 ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  overflow-x: auto;
}

.code-card .tag {
  color: #8edfd3;
  font-weight: 700;
}

.semantic-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.85rem;
}

.semantic-list article {
  padding: 1.25rem;
  border: 1px solid var(--color-line);
  border-radius: 18px;
  background: #fff;
  transition: transform 180ms var(--ease), box-shadow 180ms ease, border-color 180ms ease;
}

.semantic-list article:hover {
  border-color: rgba(15, 143, 131, 0.24);
  box-shadow: var(--shadow-sm);
  transform: translateY(-4px);
}

.semantic-list code {
  display: inline-block;
  margin-bottom: 0.75rem;
  color: var(--color-primary);
  font-size: 0.82rem;
  font-weight: 750;
}

.semantic-list p {
  margin: 0;
  color: var(--color-muted);
  font-size: 0.76rem;
  line-height: 1.65;
}

.layout-switcher {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 1.25rem;
}

.layout-options {
  display: grid;
  gap: 0.7rem;
}

.layout-option {
  display: grid;
  grid-template-columns: 62px 1fr;
  align-items: center;
  gap: 0.9rem;
  min-height: 82px;
  padding: 0.7rem;
  border: 1px solid var(--color-line);
  border-radius: 17px;
  text-align: left;
  background: #fff;
  cursor: pointer;
  transition: border-color 180ms ease, box-shadow 180ms ease, transform 180ms var(--ease);
}

.layout-option:hover {
  border-color: #bde9e2;
  transform: translateX(3px);
}

.layout-option.active {
  border-color: var(--color-primary);
  box-shadow: 0 10px 25px rgba(15, 143, 131, 0.12);
}

.layout-option > span:last-child {
  display: grid;
  gap: 0.25rem;
}

.layout-option b { font-size: 0.82rem; }
.layout-option small { color: #9299aa; font-size: 0.64rem; }

.mini-wire {
  display: grid;
  width: 62px;
  height: 50px;
  gap: 3px;
  padding: 6px;
  border-radius: 10px;
  background: #f1f3f8;
}

.mini-wire i {
  display: block;
  border-radius: 3px;
  background: #cfd6e7;
}

.layout-option.active .mini-wire { background: var(--color-blue-soft); }
.layout-option.active .mini-wire i { background: #7bd6ca; }
.mini-single { grid-template-rows: repeat(3, 1fr); }
.mini-double { grid-template-columns: 0.45fr 1fr; }
.mini-triple { grid-template-columns: 0.55fr 1fr 0.55fr; }
.mini-grid-option { grid-template-columns: repeat(2, 1fr); grid-template-rows: repeat(2, 1fr); }
.mini-card-option { grid-template-columns: repeat(3, 1fr); align-items: center; }
.mini-card-option i { height: 28px; }

.layout-stage {
  overflow: hidden;
  padding: 1rem;
}

.stage-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.15rem 0.35rem 1rem;
}

.stage-toolbar > div {
  display: flex;
  gap: 4px;
}

.stage-toolbar > div i {
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: #c3c8d4;
}

.live-dot {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  color: #7b8396;
  font-size: 0.65rem;
  font-weight: 800;
  letter-spacing: 0.12em;
}

.live-dot::before {
  display: block;
  content: "";
}

.large-wireframe {
  display: grid;
  grid-template-rows: 50px 1fr 38px;
  min-height: 380px;
  padding: 10px;
  border: 1px solid #e4e7ef;
  border-radius: 16px;
  background: #f4f5f9;
}

.wire-header {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0 0.8rem;
  border-radius: 9px;
  background: #dce3f6;
}

.wire-header i { width: 22px; height: 22px; border-radius: 7px; background: #789d98; }
.wire-header span { width: 80px; height: 6px; border-radius: 9px; background: #9eabd0; }
.wire-header b { width: 90px; height: 6px; margin-left: auto; border-radius: 9px; background: #b6c0dc; }

.wire-content {
  display: grid;
  gap: 9px;
  padding: 10px 0;
  transition: grid-template-columns 280ms var(--ease);
}

.wire-content article {
  min-width: 0;
  padding: 0.8rem;
  border: 1px solid #e0e3ea;
  border-radius: 10px;
  background: #fff;
}

.wire-content article i { display: block; height: 80px; margin-bottom: 0.75rem; border-radius: 7px; background: linear-gradient(145deg, #d9f5ef, #edf9f6); }
.wire-content article h4 { width: 55%; height: 9px; margin-bottom: 0.65rem; border-radius: 6px; background: #9ba8cc; }
.wire-content article p { width: 92%; height: 5px; margin-bottom: 0.38rem; border-radius: 6px; background: #e2e5ed; }
.wire-content article p:last-child { width: 72%; }
.wire-footer { border-radius: 8px; background: #e1e4eb; }

.layout-single .wire-content { grid-template-columns: 1fr; }
.layout-single .wire-content article:nth-child(n + 2) { display: none; }
.layout-double .wire-content { grid-template-columns: 0.45fr 1fr; }
.layout-double .wire-content article:nth-child(3) { display: none; }
.layout-triple .wire-content { grid-template-columns: 0.55fr 1.2fr 0.55fr; }
.layout-grid .wire-content { grid-template-columns: repeat(2, 1fr); }
.layout-grid .wire-content article { display: block; }
.layout-cards .wire-content { grid-template-columns: repeat(3, 1fr); align-items: center; }
.layout-cards .wire-content article { display: block; box-shadow: 0 8px 20px rgba(38, 50, 89, 0.08); }

.stage-caption {
  display: grid;
  grid-template-columns: 160px 1fr;
  align-items: center;
  gap: 1rem;
  padding: 1.2rem 0.4rem 0.3rem;
}

.stage-caption > div { display: grid; gap: 0.25rem; }
.stage-caption small { color: #969dae; font-size: 0.66rem; }
.stage-caption strong { font-size: 0.92rem; }
.stage-caption p { margin: 0; color: var(--color-muted); font-size: 0.76rem; line-height: 1.65; }

.method-cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.2rem;
}

.method-card {
  position: relative;
  min-height: 360px;
  padding: 1.5rem;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-lg);
  background: #fff;
  box-shadow: var(--shadow-sm);
  transition: transform 220ms var(--ease), box-shadow 220ms ease;
}

.method-card:hover {
  transform: translateY(-7px);
  box-shadow: var(--shadow-md);
}

.method-card.featured {
  color: #fff;
  border-color: transparent;
  background: var(--gradient-brand);
  box-shadow: var(--shadow-blue);
}

.method-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 2rem;
}

.method-top span {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border-radius: 10px;
  color: var(--color-primary);
  background: var(--color-blue-soft);
  font-size: 0.65rem;
  font-weight: 850;
}

.method-top code {
  color: #8991a3;
  font-size: 0.65rem;
}

.featured .method-top span { color: var(--color-primary); background: #fff; }
.featured .method-top code { color: rgba(255, 255, 255, 0.72); }
.method-card h3 { margin-bottom: 0.65rem; font-size: 1.4rem; }
.method-card > p { min-height: 52px; margin-bottom: 1.5rem; color: var(--color-muted); font-size: 0.78rem; line-height: 1.7; }
.featured > p { color: rgba(255, 255, 255, 0.78); }
.method-card > small { display: block; margin-top: 1rem; color: #969dae; font-size: 0.67rem; }
.featured > small { color: rgba(255, 255, 255, 0.68); }

.method-visual {
  display: flex;
  min-height: 120px;
  gap: 0.55rem;
  padding: 1rem;
  border-radius: 16px;
  background: #f3f5fa;
}

.method-visual i {
  display: grid;
  min-width: 0;
  place-items: center;
  border-radius: 9px;
  color: #0f8f83;
  background: #d9f5ef;
  font-style: normal;
  font-size: 0.73rem;
  font-weight: 800;
}

.flow-visual { flex-direction: column; }
.flow-visual i { flex: 1; }
.flex-visual { align-items: center; background: rgba(255, 255, 255, 0.13); }
.flex-visual i { flex: 1; height: 58px; color: #fff; background: rgba(255, 255, 255, 0.2); }
.grid-visual { display: grid; grid-template-columns: repeat(2, 1fr); }

.demo-lab {
  display: grid;
  grid-template-columns: 330px minmax(0, 1fr);
  min-height: 560px;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-xl);
  background: #fff;
  box-shadow: var(--shadow-md);
}

.demo-controls {
  padding: 1.7rem;
  border-right: 1px solid var(--color-line);
  background: #f9fafc;
}

.control-title {
  display: grid;
  gap: 0.35rem;
  margin-bottom: 2rem;
}

.control-title span { color: var(--color-primary); font-size: 0.66rem; font-weight: 850; letter-spacing: 0.15em; }
.control-title b { font-size: 1.4rem; }
.demo-controls fieldset { margin: 0 0 1.6rem; padding: 0; border: 0; }
.demo-controls legend { width: 100%; margin-bottom: 0.7rem; font: 0.75rem/1 ui-monospace, SFMono-Regular, Menlo, monospace; }
.demo-controls legend small { float: right; color: #939bad; font-family: inherit; }

.segmented {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 4px;
  padding: 4px;
  border-radius: 11px;
  background: #eaedf4;
}

.vertical-segments {
  grid-template-columns: repeat(2, 1fr);
}

.segmented button {
  min-height: 36px;
  padding: 0.4rem 0.3rem;
  border: 0;
  border-radius: 8px;
  color: #727b8f;
  background: transparent;
  font: 0.67rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
  cursor: pointer;
  transition: color 150ms ease, background 150ms ease, box-shadow 150ms ease;
}

.segmented button:hover { color: var(--color-primary); }
.segmented button.active { color: var(--color-primary); background: #fff; box-shadow: 0 3px 10px rgba(42, 52, 88, 0.1); }

.code-output {
  display: grid;
  gap: 0.25rem;
  padding: 1rem;
  border-radius: 13px;
  color: #8994ac;
  background: #171b27;
  font: 0.66rem/1.75 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.code-output code {
  padding-left: 1rem;
  color: #9bded4;
  white-space: pre-wrap;
}

.demo-preview {
  padding: 1.4rem;
}

.preview-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 38px;
  color: #9299aa;
  font-size: 0.64rem;
  font-weight: 750;
  letter-spacing: 0.1em;
}

.preview-label span { display: flex; align-items: center; gap: 0.5rem; }
.preview-label i { width: 6px; height: 6px; border-radius: 50%; background: #38cb89; }
.preview-label small { color: var(--color-primary); font: 0.66rem/1 ui-monospace, SFMono-Regular, Menlo, monospace; letter-spacing: 0; }

.flex-canvas {
  position: relative;
  display: flex;
  align-items: flex-start;
  justify-content: flex-start;
  height: 450px;
  gap: 0;
  padding: 4rem;
  overflow: hidden;
  border: 1px dashed #c9cfe0;
  border-radius: 20px;
  background:
    linear-gradient(#eaedf4 1px, transparent 1px),
    linear-gradient(90deg, #eaedf4 1px, transparent 1px),
    #fafbfc;
  background-size: 28px 28px;
}

.flex-item {
  display: grid;
  flex: 0 0 82px;
  height: 82px;
  place-items: center;
  border: 1px solid rgba(255, 255, 255, 0.38);
  border-radius: 17px;
  color: #fff;
  font-size: 1.1rem;
  font-weight: 850;
  box-shadow: 0 14px 25px rgba(15, 118, 110, 0.18);
  transition: transform 260ms var(--ease);
}

.item-a { background: #14b8a6; }
.item-b { background: #0f8f83; }
.item-c { background: #119b8e; }

.flex-item:hover { transform: scale(1.06); }

.axis-label {
  position: absolute;
  color: #9da4b5;
  font-size: 0.56rem;
  font-weight: 750;
  letter-spacing: 0.1em;
}

.axis-main {
  right: 2rem;
  bottom: 1.5rem;
  left: 4rem;
  display: flex;
  align-items: center;
  gap: 0.7rem;
}

.axis-main i {
  flex: 1;
  height: 1px;
  background: #bbc2d2;
}

.axis-main i::after {
  display: block;
  width: 6px;
  height: 6px;
  margin-top: -3px;
  margin-left: auto;
  border-top: 1px solid #9ba4b8;
  border-right: 1px solid #9ba4b8;
  content: "";
  transform: rotate(45deg);
}

.axis-cross {
  top: 4rem;
  right: 1rem;
  bottom: 4rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.7rem;
  writing-mode: vertical-rl;
}

.axis-cross i { flex: 1; width: 1px; background: #bbc2d2; }

.grid-lab {
  padding: 1.4rem;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-xl);
  background: #fff;
  box-shadow: var(--shadow-md);
}

.grid-toolbar {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.5rem 0.4rem 1.4rem;
}

.grid-toolbar > div > small {
  display: block;
  margin-bottom: 0.65rem;
  color: #7f8799;
  font: 0.66rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.grid-presets {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.grid-presets button {
  min-height: 38px;
  padding: 0 0.85rem;
  border: 1px solid var(--color-line);
  border-radius: 10px;
  color: #6f7789;
  background: #fff;
  font: 0.7rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
  cursor: pointer;
}

.grid-presets button:hover,
.grid-presets button.active {
  border-color: var(--color-primary);
  color: #fff;
  background: var(--color-primary);
}

.grid-toolbar > code {
  padding: 0.72rem 0.9rem;
  border-radius: 10px;
  color: #9bded4;
  background: #171b27;
  font-size: 0.67rem;
  white-space: nowrap;
}

.grid-canvas {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.8rem;
  min-height: 430px;
  padding: 1rem;
  border-radius: 20px;
  background:
    linear-gradient(#e9edf5 1px, transparent 1px),
    linear-gradient(90deg, #e9edf5 1px, transparent 1px),
    #f7f9fc;
  background-size: 24px 24px;
  transition: grid-template-columns 300ms var(--ease);
}

.grid-canvas article {
  position: relative;
  display: grid;
  min-width: 0;
  place-items: center;
  border: 1px solid rgba(15, 143, 131, 0.17);
  border-radius: 17px;
  color: var(--color-primary);
  background: linear-gradient(145deg, rgba(233, 240, 255, 0.96), rgba(240, 236, 255, 0.96));
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.6);
}

.grid-canvas article:nth-child(3n + 2) { color: #0f8f83; background: linear-gradient(145deg, #f0ecff, #e9eeff); }
.grid-canvas article:nth-child(3n) { color: #0f8f83; background: linear-gradient(145deg, #e3f8f4, #f0fdfa); }
.grid-canvas article span { position: absolute; top: 0.75rem; left: 0.85rem; color: #9ba7c7; font-size: 0.61rem; }
.grid-canvas article b { font-size: 1.6rem; }
.grid-canvas article small { margin-top: -2.5rem; color: #9099b0; font-size: 0.6rem; }

.grid-note {
  display: flex;
  align-items: center;
  gap: 0.9rem;
  padding: 1rem 0.4rem 0.2rem;
}

.grid-note > span {
  display: grid;
  flex: 0 0 38px;
  height: 38px;
  place-items: center;
  border-radius: 11px;
  color: var(--color-primary);
  background: var(--color-blue-soft);
  font-size: 0.7rem;
  font-weight: 850;
}

.grid-note p { margin: 0; color: var(--color-muted); font-size: 0.74rem; line-height: 1.65; }
.grid-note code { color: var(--color-primary); }

.centered-heading {
  grid-template-columns: minmax(0, 620px);
  justify-content: center;
  text-align: center;
}

.centered-heading .section-intro { max-width: 560px; margin: 0 auto; }

.principle-cards {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1rem;
}

.principle-cards article {
  position: relative;
  min-height: 310px;
  padding: 1.35rem;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-lg);
  background: #fff;
  transition: transform 220ms var(--ease), box-shadow 220ms ease, border-color 220ms ease;
}

.principle-cards article:hover {
  border-color: rgba(15, 143, 131, 0.25);
  box-shadow: var(--shadow-md);
  transform: translateY(-7px);
}

.principle-cards article > span {
  position: absolute;
  top: 1.35rem;
  right: 1.35rem;
  color: #b0b7c6;
  font-size: 0.64rem;
  font-weight: 800;
}

.principle-cards h3 { margin-bottom: 0.65rem; font-size: 1.05rem; }
.principle-cards h3 small { display: block; margin-top: 0.28rem; color: #9ba2b2; font-size: 0.58rem; font-weight: 600; letter-spacing: 0.08em; text-transform: uppercase; }
.principle-cards p { margin: 0; color: var(--color-muted); font-size: 0.74rem; line-height: 1.65; }

.principle-icon {
  position: relative;
  width: 100%;
  height: 130px;
  margin-bottom: 1.25rem;
  overflow: hidden;
  border-radius: 16px;
  background: var(--gradient-soft);
}

.align-icon i { position: absolute; left: 28px; width: 55%; height: 11px; border-radius: 5px; background: #8edfd3; }
.align-icon i:nth-child(1) { top: 30px; width: 68%; }
.align-icon i:nth-child(2) { top: 59px; width: 42%; }
.align-icon i:nth-child(3) { top: 88px; width: 57%; }
.align-icon::before { position: absolute; top: 20px; bottom: 20px; left: 20px; width: 2px; border-radius: 2px; background: #14b8a6; content: ""; }

.spacing-icon i { position: absolute; top: 35px; width: 42px; height: 62px; border-radius: 9px; background: #bde9e2; }
.spacing-icon i:first-child { left: 22px; }
.spacing-icon i:nth-child(2) { right: 22px; }
.spacing-icon b { position: absolute; top: 54px; left: 50%; color: var(--color-primary); font-size: 1.1rem; transform: translateX(-50%); }

.hierarchy-icon { display: flex; align-items: center; justify-content: center; gap: 0.8rem; color: var(--color-primary); }
.hierarchy-icon b { font-size: 3rem; }
.hierarchy-icon i { font-style: normal; font-size: 1.7rem; font-weight: 750; }
.hierarchy-icon small { font-size: 0.9rem; font-weight: 750; }

.consistency-icon { display: grid; grid-template-columns: repeat(2, 42px); grid-template-rows: repeat(2, 38px); align-content: center; justify-content: center; gap: 8px; }
.consistency-icon i { border: 2px solid #99d8cf; border-radius: 8px; background: rgba(255, 255, 255, 0.7); }

.responsive-lab {
  display: grid;
  grid-template-columns: 170px minmax(0, 1fr);
  min-height: 650px;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-xl);
  background: #fff;
  box-shadow: var(--shadow-md);
}

.device-selector {
  display: grid;
  align-content: center;
  gap: 1.8rem;
  padding: 2rem 1rem;
  border-right: 1px solid var(--color-line);
  background: #fafbfc;
}

.device {
  display: grid;
  justify-items: center;
  gap: 0.35rem;
  color: #a1a8b7;
  transition: color 180ms ease, transform 180ms ease;
}

.device.active { color: var(--color-primary); transform: scale(1.05); }
.device b { font-size: 0.73rem; }
.device small { font-size: 0.57rem; }
.device i { position: relative; display: grid; place-items: center; border: 2px solid currentColor; border-radius: 6px; }
.device i span { display: block; width: 68%; height: 50%; border-radius: 2px; background: currentColor; opacity: 0.2; }
.desktop-device i { width: 56px; height: 38px; }
.desktop-device i::after { position: absolute; bottom: -8px; width: 23px; height: 6px; border-top: 2px solid currentColor; content: ""; }
.tablet-device i { width: 40px; height: 48px; }
.mobile-device i { width: 27px; height: 48px; }

.responsive-workspace {
  display: grid;
  grid-template-rows: auto 1fr auto;
  min-width: 0;
  padding: 1.5rem;
}

.responsive-topline {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0 0.2rem 1.2rem;
}

.responsive-topline > div { display: flex; align-items: baseline; gap: 0.6rem; }
.responsive-topline span { color: #969dae; font-size: 0.6rem; font-weight: 800; letter-spacing: 0.12em; }
.responsive-topline strong { font-size: 0.85rem; }
.responsive-topline code { padding: 0.5rem 0.7rem; border-radius: 8px; color: #0f8f83; background: var(--color-blue-soft); font-size: 0.64rem; }

.viewport-track {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 500px;
  padding: 1.2rem;
  overflow: hidden;
  border-radius: 20px;
  background:
    linear-gradient(#e9ecf3 1px, transparent 1px),
    linear-gradient(90deg, #e9ecf3 1px, transparent 1px),
    #f5f7fa;
  background-size: 24px 24px;
}

.viewport-shell {
  width: 100%;
  max-width: 760px;
  overflow: hidden;
  border: 1px solid #cbd1dd;
  border-radius: 14px;
  background: #fff;
  box-shadow: 0 18px 45px rgba(44, 54, 93, 0.16);
  transition: width 220ms var(--ease), border-radius 220ms ease;
}

.viewport-browser {
  display: flex;
  align-items: center;
  gap: 4px;
  height: 28px;
  padding: 0 0.6rem;
  border-bottom: 1px solid #e5e8ef;
  background: #f7f8fa;
}

.viewport-browser i { width: 5px; height: 5px; border-radius: 50%; background: #c8cdd8; }
.viewport-browser span { margin-left: 0.5rem; color: #a2a9b8; font-size: 0.48rem; }
.viewport-page { padding: 0.75rem; }
.viewport-page header { display: flex; align-items: center; height: 38px; padding: 0 0.65rem; border-radius: 7px; background: #e3f8f4; }
.viewport-page header b { width: 44px; height: 8px; border-radius: 3px; background: #0f8f83; }
.viewport-page header nav { display: flex; gap: 7px; margin-left: auto; }
.viewport-page header nav i { width: 28px; height: 4px; border-radius: 3px; background: #9aabe6; }
.viewport-page main { display: grid; grid-template-columns: 1fr 0.9fr; gap: 0.8rem; min-height: 210px; padding: 1.5rem 0.7rem; }
.vp-copy { align-content: center; display: grid; }
.vp-copy small { width: 40px; height: 5px; margin-bottom: 0.6rem; border-radius: 3px; background: #14b8a6; }
.vp-copy h4 { width: 75%; height: 22px; margin-bottom: 0.65rem; border-radius: 4px; background: #424b64; }
.vp-copy p { width: 90%; height: 5px; margin-bottom: 0.4rem; border-radius: 4px; background: #d9dde6; }
.vp-copy p:nth-of-type(2) { width: 70%; }
.vp-copy button { width: 55px; height: 20px; margin-top: 0.6rem; border: 0; border-radius: 5px; background: #0f8f83; }
.vp-image { border-radius: 10px; background: linear-gradient(145deg, #d9f5ef, #e9faf6); }
.viewport-page section { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0.55rem; }
.viewport-page section article { height: 75px; border: 1px solid #e0e4ed; border-radius: 8px; background: #f6f7fa; }

.viewport-shell.mode-tablet .viewport-page main { grid-template-columns: 1fr 0.75fr; }
.viewport-shell.mode-tablet .viewport-page section { grid-template-columns: repeat(2, 1fr); }
.viewport-shell.mode-tablet .viewport-page section article:last-child { grid-column: 1 / -1; }
.viewport-shell.mode-mobile { border-radius: 21px; }
.viewport-shell.mode-mobile .viewport-page { padding: 0.55rem; }
.viewport-shell.mode-mobile .viewport-page header nav i:not(:first-child) { display: none; }
.viewport-shell.mode-mobile .viewport-page header nav i:first-child { width: 14px; height: 11px; border-top: 2px solid #7daaa3; border-bottom: 2px solid #7daaa3; border-radius: 0; background: transparent; }
.viewport-shell.mode-mobile .viewport-page main { grid-template-columns: 1fr; gap: 0.6rem; padding: 0.8rem 0.2rem; }
.viewport-shell.mode-mobile .vp-image { min-height: 100px; grid-row: 1; }
.viewport-shell.mode-mobile .viewport-page section { grid-template-columns: 1fr; }
.viewport-shell.mode-mobile .viewport-page section article:last-child { grid-column: auto; }

.range-wrap {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.8rem;
  padding: 1.4rem 0.4rem 0;
  color: #8f97a9;
  font-size: 0.65rem;
}

.range-wrap input {
  width: 100%;
  height: 5px;
  border-radius: 999px;
  outline: none;
  background: linear-gradient(90deg, #dcece9, #14b8a6);
  appearance: none;
}

.range-wrap input::-webkit-slider-thumb {
  width: 20px;
  height: 20px;
  border: 4px solid #fff;
  border-radius: 50%;
  background: var(--color-primary);
  box-shadow: 0 2px 8px rgba(15, 143, 131, 0.35);
  cursor: ew-resize;
  appearance: none;
}

.summary-section {
  padding-top: var(--section-space);
  padding-bottom: 4rem;
  background: #fff;
}

.summary-card {
  position: relative;
  display: grid;
  grid-template-columns: 1.2fr 1fr auto;
  align-items: center;
  gap: 2.5rem;
  min-height: 330px;
  padding: 3.5rem;
  overflow: hidden;
  border-radius: var(--radius-xl);
  color: #fff;
  background:
    radial-gradient(circle at 10% 120%, rgba(98, 230, 210, 0.45), transparent 25rem),
    radial-gradient(circle at 90% -20%, rgba(189, 239, 230, 0.55), transparent 24rem),
    linear-gradient(125deg, #0f8f83, #0a8a7f 62%, #087f76);
  box-shadow: 0 28px 60px rgba(15, 118, 110, 0.28);
}

.summary-heading { position: relative; z-index: 1; }
.summary-heading > span { display: inline-block; margin-bottom: 1rem; color: #ccfbf1; font-size: 0.68rem; font-weight: 850; letter-spacing: 0.16em; }
.summary-heading h2 { margin-bottom: 0.85rem; font-size: clamp(2.5rem, 4vw, 4rem); letter-spacing: -0.05em; }
.summary-heading p { max-width: 420px; margin: 0; color: rgba(255, 255, 255, 0.72); font-size: 0.82rem; line-height: 1.75; }

.checklist {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.8rem 1.3rem;
}

.checklist div { display: flex; align-items: center; gap: 0.55rem; font-size: 0.77rem; white-space: nowrap; }
.checklist span { display: grid; width: 22px; height: 22px; place-items: center; border-radius: 50%; color: #fff; background: rgba(255, 255, 255, 0.17); font-size: 0.7rem; }

.button-light { position: relative; z-index: 1; color: var(--color-primary); background: #fff; box-shadow: 0 14px 30px rgba(22, 28, 98, 0.2); white-space: nowrap; }
.summary-orb { position: absolute; inset: 0; pointer-events: none; }
.summary-orb i { position: absolute; border: 1px solid rgba(255, 255, 255, 0.12); border-radius: 50%; }
.summary-orb i:nth-child(1) { top: -150px; right: -80px; width: 380px; height: 380px; }
.summary-orb i:nth-child(2) { top: -80px; right: -10px; width: 240px; height: 240px; }
.summary-orb i:nth-child(3) { bottom: -100px; left: 35%; width: 190px; height: 190px; }

.chapter-navigation {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 2rem;
  padding-top: 2.2rem;
  padding-bottom: 4rem;
  background: #fff;
}

.chapter-link {
  display: flex;
  align-items: center;
  gap: 1rem;
  width: fit-content;
  padding: 0.8rem;
  border-radius: 14px;
  transition: background 180ms ease, transform 180ms ease;
}

.chapter-link:hover { background: var(--color-blue-soft); transform: translateX(3px); }
.chapter-link.previous:hover { transform: translateX(-3px); }
.chapter-link.next { justify-self: end; text-align: right; }
.chapter-link.disabled { opacity: 0.4; pointer-events: none; }
.chapter-link > span { display: grid; width: 42px; height: 42px; place-items: center; border: 1px solid var(--color-line); border-radius: 12px; color: var(--color-primary); background: #fff; }
.chapter-link div { display: grid; gap: 0.2rem; }
.chapter-link small { color: #999faf; font-size: 0.57rem; font-weight: 750; letter-spacing: 0.12em; }
.chapter-link b { font-size: 0.8rem; }

.chapter-position { display: grid; min-width: 180px; justify-items: center; gap: 0.35rem; }
.chapter-position small { color: #a0a7b6; font-size: 0.56rem; font-weight: 750; letter-spacing: 0.12em; }
.chapter-position strong { font-size: 0.86rem; }
.chapter-position strong span { color: #9ba2b2; font-weight: 500; }
.chapter-position > div { width: 100%; height: 4px; margin-top: 0.3rem; overflow: hidden; border-radius: 999px; background: #e8ebf2; }
.chapter-position > div i { display: block; width: 10%; height: 100%; border-radius: inherit; background: var(--gradient-brand); }

@media (max-width: 1100px) {
  .hero { grid-template-columns: 0.8fr 1.2fr; gap: 1.5rem; }
  .hero h1 { font-size: clamp(3.6rem, 6.5vw, 5rem); }
  .principle-cards { grid-template-columns: repeat(2, 1fr); }
  .summary-card { grid-template-columns: 1fr 1fr; }
  .summary-card .button-light { grid-column: 1 / -1; justify-self: start; }
}

@media (max-width: 900px) {
  .hero { grid-template-columns: 1fr; min-height: auto; padding-top: 4rem; }
  .hero-copy { text-align: center; }
  .chapter-kicker, .hero-actions, .hero-meta { justify-content: center; }
  .hero-copy > p { margin-right: auto; margin-left: auto; }
  .hero-visual { width: min(100%, 680px); min-height: 500px; margin: 0 auto; }
  .concept-grid, .structure-grid { grid-template-columns: 1fr; }
  .layout-switcher { grid-template-columns: 1fr; }
  .layout-options { grid-template-columns: repeat(5, 1fr); }
  .layout-option { grid-template-columns: 1fr; justify-items: center; min-height: 125px; text-align: center; }
  .method-cards { grid-template-columns: 1fr; }
  .method-card { min-height: 300px; }
  .demo-lab { grid-template-columns: 1fr; }
  .demo-controls { border-right: 0; border-bottom: 1px solid var(--color-line); }
  .responsive-lab { grid-template-columns: 1fr; }
  .device-selector { grid-template-columns: repeat(3, 1fr); border-right: 0; border-bottom: 1px solid var(--color-line); }
  .summary-card { padding: 2.5rem; }
}

@media (max-width: 700px) {
  .learning-strip { justify-content: flex-start; overflow-x: auto; }
  .learning-strip > span { display: none; }
  .layout-options { display: flex; padding-bottom: 0.4rem; overflow-x: auto; }
  .layout-option { flex: 0 0 140px; }
  .large-wireframe { min-height: 340px; }
  .stage-caption { grid-template-columns: 1fr; }
  .semantic-list { grid-template-columns: 1fr; }
  .principle-cards { grid-template-columns: 1fr; }
  .principle-cards article { min-height: 280px; }
  .grid-toolbar { align-items: flex-start; flex-direction: column; }
  .grid-toolbar > code { max-width: 100%; overflow: auto; }
  .responsive-topline { align-items: flex-start; flex-direction: column; }
  .chapter-navigation { grid-template-columns: 1fr 1fr; }
  .chapter-position { grid-column: 1 / -1; grid-row: 1; }
  .chapter-link.previous { grid-column: 1; }
  .chapter-link.next { grid-column: 2; }
  .summary-card { grid-template-columns: 1fr; }
  .summary-card .button-light { grid-column: auto; }
}

@media (max-width: 560px) {
  .hero { padding-top: 3rem; padding-bottom: 4.5rem; }
  .chapter-kicker { font-size: 0.63rem; }
  .hero h1 { font-size: 3.55rem; }
  .hero-visual { min-height: 390px; margin-top: 1rem; }
  .browser-card { top: 30px; left: 0; width: 100%; }
  .browser-bar { height: 44px; }
  .browser-layout { grid-template-columns: 0.45fr 1.5fr; grid-template-rows: 52px 220px 45px; gap: 5px; padding: 7px; }
  .region-aside { display: none; }
  .region-footer { grid-column: 1 / -1; }
  .region-header i { width: 20px; }
  .content-cards { grid-template-columns: repeat(2, 1fr); }
  .content-cards i { height: 70px; }
  .content-cards i:last-child { display: none; }
  .floating-card { min-width: 135px; padding: 0.65rem; }
  .floating-code { right: -0.4rem; }
  .floating-grid { right: 0; bottom: 0; }
  .floating-card > span:first-child { width: 32px; height: 32px; }
  .anatomy-diagram { grid-template-rows: 65px 45px 190px 55px; min-height: 390px; }
  .anatomy-body { grid-template-columns: 1.7fr 0.8fr; }
  .code-card pre { padding: 1.5rem 1.2rem; font-size: 0.76rem; }
  .layout-stage { padding: 0.65rem; }
  .large-wireframe { min-height: 300px; }
  .layout-triple .wire-content, .layout-cards .wire-content { gap: 4px; }
  .wire-content article { padding: 0.45rem; }
  .wire-content article i { height: 62px; }
  .demo-lab, .grid-lab, .responsive-lab { border-radius: 23px; }
  .demo-controls { padding: 1.25rem; }
  .demo-preview { padding: 0.8rem; }
  .flex-canvas { height: 380px; padding: 3rem 1.5rem; }
  .flex-item { flex-basis: 62px; height: 62px; border-radius: 14px; }
  .axis-main { left: 1.5rem; }
  .grid-lab { padding: 0.75rem; }
  .grid-canvas { min-height: 380px; padding: 0.65rem; gap: 0.5rem; }
  .grid-canvas article small { display: none; }
  .device-selector { gap: 0.6rem; padding: 1.2rem 0.6rem; }
  .responsive-workspace { padding: 0.8rem; }
  .viewport-track { min-height: 450px; padding: 0.7rem; }
  .viewport-shell.mode-mobile { max-width: none; }
  .summary-section { padding-top: 5rem; }
  .summary-card { gap: 2rem; padding: 2rem 1.35rem; border-radius: 24px; }
  .checklist { grid-template-columns: 1fr; }
  .chapter-link div { display: none; }
  .chapter-link > span { width: 48px; height: 48px; }
}

/* Chapter workspace: one learning unit at a time */
.course-workspace {
  display: none;
  min-height: 0;
  gap: 0.85rem;
  padding: 0.85rem 1.25rem 1.25rem;
  background: #f3f5fa;
}

body.study-mode {
  min-height: 100dvh;
  overflow: hidden;
}

body.study-mode .page-frame {
  height: calc(100dvh - 1rem);
  margin-top: 0.5rem;
  margin-bottom: 0.5rem;
}

body.study-mode .page-shell {
  display: grid;
  grid-template-rows: auto minmax(0, 1fr);
  height: 100%;
}

body.study-mode main {
  min-height: 0;
}

body.study-mode .hero,
body.study-mode .learning-strip,
body.study-mode .site-footer,
body.study-mode .scroll-progress,
body.study-mode .back-to-top {
  display: none;
}

body.study-mode .course-workspace {
  display: grid;
  grid-template-columns: 226px minmax(0, 1fr);
  height: 100%;
}

.lesson-sidebar {
  display: grid;
  grid-template-rows: auto minmax(0, 1fr) auto;
  min-height: 0;
  padding: 1.25rem 0.75rem 0.85rem;
  overflow: hidden;
  border: 1px solid rgba(15, 143, 131, 0.09);
  border-radius: 22px;
  background:
    radial-gradient(circle at 15% 0%, rgba(20, 184, 166, 0.09), transparent 11rem),
    #fff;
  box-shadow: var(--shadow-sm);
}

.sidebar-heading {
  padding: 0.35rem 0.6rem 1rem;
}

.sidebar-heading > span {
  color: var(--color-primary);
  font-size: 0.59rem;
  font-weight: 850;
  letter-spacing: 0.16em;
}

.sidebar-heading h2 {
  margin: 0.55rem 0 0.85rem;
  font-size: 1.3rem;
  line-height: 1.22;
  letter-spacing: -0.035em;
}

.sidebar-heading p {
  margin: 0;
  color: #a0a8b8;
  font-size: 0.54rem;
  font-weight: 800;
  letter-spacing: 0.14em;
}

.lesson-menu {
  display: grid;
  align-content: start;
  gap: 0.3rem;
  min-height: 0;
  padding: 0.2rem 0.1rem;
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: #d9def1 transparent;
}

.lesson-menu button {
  display: grid;
  grid-template-columns: 30px minmax(0, 1fr) auto;
  align-items: center;
  gap: 0.55rem;
  width: 100%;
  min-height: 48px;
  padding: 0.45rem 0.55rem;
  border: 1px solid transparent;
  border-radius: 12px;
  text-align: left;
  background: transparent;
  cursor: pointer;
  transition: border-color 160ms ease, background 160ms ease, transform 160ms var(--ease);
}

.lesson-menu button:hover {
  border-color: #e3e7f2;
  background: #f8f9fc;
  transform: translateX(2px);
}

.lesson-menu button > span {
  display: grid;
  width: 30px;
  height: 30px;
  place-items: center;
  border-radius: 9px;
  color: #8e96a8;
  background: #f0f2f6;
  font-size: 0.59rem;
  font-weight: 800;
}

.lesson-menu button > div {
  display: grid;
  gap: 0.14rem;
}

.lesson-menu button b {
  font-size: 0.72rem;
}

.lesson-menu button small {
  color: #a2a9b8;
  font-size: 0.52rem;
}

.lesson-menu button > i {
  color: #aab1c0;
  font-style: normal;
  font-size: 0.72rem;
  opacity: 0;
  transform: translateX(-4px);
  transition: opacity 160ms ease, transform 160ms ease;
}

.lesson-menu button.active {
  border-color: rgba(15, 143, 131, 0.15);
  color: var(--color-primary);
  background: var(--color-blue-soft);
}

.lesson-menu button.active > span {
  color: #fff;
  background: var(--gradient-brand);
  box-shadow: 0 6px 13px rgba(15, 143, 131, 0.22);
}

.lesson-menu button.active > i {
  color: var(--color-primary);
  opacity: 1;
  transform: translateX(0);
}

.sidebar-progress {
  padding: 0.8rem 0.6rem 0.2rem;
}

.sidebar-progress > div:first-child {
  display: flex;
  justify-content: space-between;
  margin-bottom: 0.55rem;
  color: #9299aa;
  font-size: 0.58rem;
}

.sidebar-progress strong {
  color: var(--color-primary);
}

.sidebar-progress > div:last-child {
  height: 4px;
  overflow: hidden;
  border-radius: 99px;
  background: #eaedf3;
}

.sidebar-progress i {
  display: block;
  width: 11.111%;
  height: 100%;
  border-radius: inherit;
  background: var(--gradient-brand);
  transition: width 240ms var(--ease);
}

.lesson-viewport {
  display: grid;
  grid-template-rows: 64px minmax(0, 1fr) 64px;
  min-width: 0;
  min-height: 0;
  overflow: hidden;
  border: 1px solid var(--color-line);
  border-radius: 24px;
  background: #fff;
  box-shadow: var(--shadow-md);
}

.lesson-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0 1.35rem;
  border-bottom: 1px solid var(--color-line);
  background: rgba(255, 255, 255, 0.95);
}

.lesson-toolbar > div {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
}

.lesson-toolbar span {
  color: var(--color-primary);
  font-size: 0.58rem;
  font-weight: 850;
  letter-spacing: 0.12em;
}

.lesson-toolbar strong {
  font-size: 0.82rem;
}

.lesson-toolbar button {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  min-height: 36px;
  padding: 0 0.7rem;
  border: 1px solid var(--color-line);
  border-radius: 10px;
  color: #6f7789;
  background: #fff;
  font-size: 0.66rem;
  cursor: pointer;
}

.lesson-toolbar button:hover {
  border-color: #bde9e2;
  color: var(--color-primary);
  background: var(--color-blue-soft);
}

.lesson-toolbar svg,
.lesson-pagination svg {
  width: 16px;
  fill: none;
  stroke: currentColor;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 1.8;
}

.lesson-pages {
  position: relative;
  min-height: 0;
  overflow: hidden;
}

.lesson-pages > .course-page {
  display: none !important;
  height: 100%;
  min-height: 0;
  padding: 1.8rem clamp(1.4rem, 3vw, 2.6rem);
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: #cfd6e9 transparent;
}

.lesson-pages > .course-page.active {
  display: block !important;
  animation: lesson-enter 260ms var(--ease) both;
}

@keyframes lesson-enter {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.course-workspace .section-heading {
  gap: 1.5rem;
  margin-bottom: 1.7rem;
}

.course-workspace .section-heading h2 {
  font-size: clamp(2rem, 3.4vw, 3.25rem);
}

.course-workspace .section-number {
  top: -0.75rem;
  font-size: clamp(4.5rem, 7vw, 6.5rem);
}

.course-workspace .section-intro {
  font-size: 0.82rem;
  line-height: 1.7;
}

.course-workspace .anatomy-diagram {
  grid-template-rows: 62px 42px 180px 48px;
  min-height: 360px;
}

.course-workspace .anatomy-diagram > .anatomy-body {
  display: grid;
  align-items: stretch;
  justify-content: stretch;
}

.course-workspace .region-list article {
  min-height: 67px;
}

.course-workspace .method-card {
  min-height: 285px;
}

.course-workspace .method-top {
  margin-bottom: 1.2rem;
}

.course-workspace .method-visual {
  min-height: 90px;
}

.course-workspace .demo-lab {
  min-height: 445px;
}

.course-workspace .flex-canvas {
  height: 340px;
}

.course-workspace .grid-canvas {
  min-height: 330px;
}

.course-workspace .responsive-lab {
  min-height: 500px;
}

.course-workspace .viewport-track {
  min-height: 350px;
}

.lesson-pagination {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1rem;
  padding: 0 1rem;
  border-top: 1px solid var(--color-line);
  background: #fff;
}

.lesson-pagination > button {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  width: fit-content;
  padding: 0.42rem 0.65rem;
  border: 0;
  border-radius: 10px;
  background: transparent;
  cursor: pointer;
}

.lesson-pagination > button:last-child {
  justify-self: end;
  text-align: right;
}

.lesson-pagination > button:hover:not(:disabled) {
  color: var(--color-primary);
  background: var(--color-blue-soft);
}

.lesson-pagination > button:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.lesson-pagination button span {
  display: grid;
  gap: 0.1rem;
}

.lesson-pagination small {
  color: #9ba2b2;
  font-size: 0.49rem;
  font-weight: 800;
  letter-spacing: 0.09em;
}

.lesson-pagination b {
  font-size: 0.68rem;
}

.lesson-pagination > div {
  display: grid;
  grid-template-columns: auto 120px auto;
  align-items: center;
  gap: 0.6rem;
  color: #8f97a8;
  font-size: 0.57rem;
}

.lesson-pagination > div > i {
  height: 4px;
  overflow: hidden;
  border-radius: 99px;
  background: #e9ecf2;
}

.lesson-pagination > div > i b {
  display: block;
  width: 11.111%;
  height: 100%;
  border-radius: inherit;
  background: var(--gradient-brand);
  transition: width 240ms var(--ease);
}

.course-workspace .summary-section {
  background: #f7f8fb;
}

.course-workspace .summary-card {
  grid-template-columns: 1.15fr 1fr auto;
  min-height: 100%;
  padding: clamp(2rem, 4vw, 3.5rem);
}

.summary-chapter-links {
  position: relative;
  z-index: 1;
  display: grid;
  grid-column: 1 / -1;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1rem;
  padding-top: 1.2rem;
  border-top: 1px solid rgba(255, 255, 255, 0.16);
}

.summary-chapter-links button {
  width: fit-content;
  padding: 0.6rem 0.8rem;
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: 10px;
  color: #fff;
  background: rgba(255, 255, 255, 0.1);
  font-size: 0.68rem;
  cursor: pointer;
}

.summary-chapter-links button:last-child {
  justify-self: end;
}

.summary-chapter-links button:hover:not(:disabled) {
  background: rgba(255, 255, 255, 0.2);
}

.summary-chapter-links button:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.summary-chapter-links > strong {
  font-size: 0.72rem;
}

.summary-chapter-links small {
  color: rgba(255, 255, 255, 0.55);
}

@media (max-width: 900px) {
  body.study-mode .page-frame {
    height: calc(100dvh - 1rem);
  }

  body.study-mode .course-workspace {
    grid-template-rows: auto minmax(0, 1fr);
    grid-template-columns: 1fr;
    gap: 0.55rem;
    padding: 0.55rem 0.65rem 0.65rem;
  }

  .lesson-sidebar {
    display: block;
    padding: 0.45rem;
    border-radius: 16px;
  }

  .sidebar-heading,
  .sidebar-progress {
    display: none;
  }

  .lesson-menu {
    display: flex;
    gap: 0.35rem;
    padding: 0;
    overflow-x: auto;
  }

  .lesson-menu button {
    grid-template-columns: 26px auto;
    flex: 0 0 auto;
    width: auto;
    min-height: 42px;
    padding: 0.3rem 0.55rem;
  }

  .lesson-menu button > span {
    width: 26px;
    height: 26px;
    border-radius: 8px;
  }

  .lesson-menu button > i,
  .lesson-menu button small {
    display: none;
  }

  .lesson-viewport {
    grid-template-rows: 56px minmax(0, 1fr) 58px;
    border-radius: 18px;
  }

  .course-workspace .summary-card {
    grid-template-columns: 1fr 1fr;
  }

  .course-workspace .summary-card .button-light {
    grid-column: 1 / -1;
  }

  .case-brief { grid-template-columns: 1fr 1fr; }
  .case-brief > div { grid-column: 1 / -1; }
}

@media (max-width: 560px) {
  body.study-mode .page-frame {
    width: calc(100% - 0.5rem);
    height: calc(100dvh - 0.5rem);
    margin: 0.25rem;
    padding: 4px;
  }

  body.study-mode .site-header {
    padding: 0.4rem 0.4rem 0;
  }

  body.study-mode .navbar {
    min-height: 54px;
  }

  body.study-mode .course-workspace {
    padding: 0.4rem;
  }

  .lesson-menu button b {
    font-size: 0.66rem;
  }

  .lesson-toolbar {
    padding: 0 0.8rem;
  }

  .lesson-toolbar > div {
    display: grid;
    gap: 0.15rem;
  }

  .lesson-toolbar strong {
    max-width: 185px;
    overflow: hidden;
    font-size: 0.72rem;
    text-overflow: ellipsis;
    white-space: nowrap;
  }

  .lesson-toolbar button {
    width: 38px;
    padding: 0;
    justify-content: center;
    overflow: hidden;
    color: transparent;
    font-size: 0;
  }

  .lesson-toolbar button svg {
    color: var(--color-primary);
  }

  .lesson-pages > .course-page {
    padding: 1.6rem 0.85rem;
  }

  .course-workspace .section-heading {
    margin-bottom: 1.4rem;
  }

  .course-workspace .section-heading h2 {
    font-size: 2rem;
  }

  .course-workspace .demo-lab,
  .course-workspace .responsive-lab {
    min-height: auto;
  }

  .lesson-pagination > div {
    grid-template-columns: auto 72px auto;
  }

  .lesson-pagination button span {
    display: none;
  }

  .lesson-pagination > button {
    display: grid;
    width: 38px;
    height: 38px;
    place-items: center;
    padding: 0;
    border: 1px solid var(--color-line);
  }

  .course-workspace .summary-card {
    grid-template-columns: 1fr;
    gap: 1.5rem;
    min-height: 0;
    padding: 1.6rem 1.15rem;
  }

  .course-workspace .summary-card .button-light,
  .summary-chapter-links {
    grid-column: auto;
  }

  .summary-chapter-links {
    grid-template-columns: 1fr 1fr;
  }

  .summary-chapter-links > strong {
    grid-column: 1 / -1;
    grid-row: 1;
    text-align: center;
  }

  .case-step {
    grid-template-columns: 1fr;
    gap: 0.55rem;
  }

  .case-step > span { justify-self: start; }
  .case-step > div { display: grid; gap: 0.25rem; }
  .case-brief,
  .theory-pair,
  .theory-band { grid-template-columns: 1fr; }
  .case-brief > div { grid-column: auto; }
  .journey-result { grid-template-columns: 1fr; }
}

/* Keep the teaching-view controls above the chapter toolbar's generic button rules. */
.lesson-toolbar .lesson-mode-tabs {
  display: inline-flex;
  align-items: center;
  gap: 0.2rem;
}

.lesson-toolbar .lesson-mode-tabs[hidden] { display: none !important; }

.lesson-toolbar .lesson-mode-tabs button {
  width: auto;
  min-height: 30px;
  padding: 0 0.8rem;
  overflow: visible;
  border: 0;
  color: #7b8497;
  background: transparent;
  font-size: 0.64rem;
}

.lesson-toolbar .lesson-mode-tabs button:hover { color: var(--color-primary); }
.lesson-toolbar .lesson-mode-tabs button.active { color: #fff; background: var(--gradient-brand); }

@media (max-width: 560px) {
  .lesson-toolbar-title { display: none !important; }
  .lesson-toolbar .lesson-mode-tabs { margin-right: auto; }
  .lesson-toolbar .lesson-mode-tabs button {
    display: inline-flex;
    width: auto;
    min-width: 50px;
    padding: 0 0.6rem;
    color: #7b8497;
    font-size: 0.6rem;
  }
  .lesson-toolbar .lesson-mode-tabs button.active { color: #fff; }
}

/* Chapter 01 mint/teal palette. Color-only overrides keep the existing layout intact. */
:root {
  --color-primary: #14b8a6;
  --color-secondary: #0f8f83;
  --color-purple: #0f8f83;
  --color-blue-soft: #f0fdfa;
  --color-bg: #f8fbfa;
  --color-surface: rgba(255, 255, 255, 0.82);
  --color-cream: #f8fbfa;
  --color-ink: #111111;
  --color-muted: #64748b;
  --color-line: rgba(15, 143, 131, 0.12);
  --color-line-strong: #dcece9;
  --gradient-brand: linear-gradient(110deg, #62e6d2 0%, #24c8b3 35%, #119b8e 70%, #087f76 100%);
  --gradient-frame: linear-gradient(145deg, #bdefe6 0%, #48cdbb 48%, #0f8f83 100%);
  --gradient-text: linear-gradient(135deg, #20c7b4 0%, #0fa394 55%, #087e75 100%);
  --gradient-soft: linear-gradient(145deg, #f0fdfa 0%, #eaf9f6 100%);
  --shadow-sm: 0 8px 24px rgba(15, 118, 110, 0.06);
  --shadow-md: 0 18px 50px rgba(15, 118, 110, 0.09);
  --shadow-blue: 0 18px 40px rgba(15, 118, 110, 0.1);
}

body {
  color: #111111;
  background:
    radial-gradient(circle at 5% 12%, rgba(216, 247, 240, 0.3), transparent 24rem),
    radial-gradient(circle at 96% 88%, rgba(189, 239, 230, 0.22), transparent 28rem),
    #f8fbfa;
}

.page-frame {
  background: var(--gradient-frame);
  box-shadow: 0 30px 90px rgba(15, 118, 110, 0.1);
}

.page-shell,
.summary-section,
.chapter-navigation {
  background-color: #f8fbfa;
}

.navbar {
  background: linear-gradient(110deg, #62e6d2 0%, #24c8b3 35%, #119b8e 70%, #087f76 100%);
  box-shadow: 0 16px 36px rgba(15, 118, 110, 0.13);
}

.chapter-pill,
.language-switch button.active {
  color: #0f8f83;
  box-shadow: 0 8px 24px rgba(15, 118, 110, 0.11);
}

.gradient-text {
  background: linear-gradient(135deg, #20c7b4 0%, #0fa394 55%, #087e75 100%);
  -webkit-background-clip: text;
  background-clip: text;
}

.button-primary {
  background: linear-gradient(135deg, #12b8a6, #07947f);
  box-shadow: 0 12px 28px rgba(15, 118, 110, 0.12);
}

.button-primary:hover {
  background: linear-gradient(135deg, #0fae9d, #078a77);
  box-shadow: 0 15px 32px rgba(15, 118, 110, 0.15);
}

.button-secondary:hover {
  border-color: rgba(15, 143, 131, 0.22);
  background: #f0fdfa;
}

.hero {
  background:
    radial-gradient(circle at 80% 28%, rgba(216, 247, 240, 0.28), transparent 25rem),
    radial-gradient(circle at 5% 80%, rgba(189, 239, 230, 0.2), transparent 24rem);
}

.orbit {
  border-color: rgba(15, 143, 131, 0.12);
}

.browser-card {
  border-color: #dcece9;
  background: rgba(255, 255, 255, 0.94);
  box-shadow: 0 20px 50px rgba(15, 118, 110, 0.1), 18px 18px 0 rgba(216, 247, 240, 0.25);
}

.browser-bar,
.browser-layout {
  border-color: #dcece9;
  background-color: #f8fbfa;
}

.region {
  border-color: #dcece9;
  color: #64748b;
  background: #f0fdfa;
}

.region-header {
  color: #0f8f83;
  background: #e3f8f4;
}

.region-header i { background: rgba(15, 143, 131, 0.2); }
.region-sidebar,
.region-aside { background: #f8fbfa; }
.region-main { background: rgba(255, 255, 255, 0.96); }
.content-lines i { background: #dcece9; }
.content-cards i { background: linear-gradient(145deg, #d9f5ef, #f0fdfa); }
.region-footer { color: #94a3b8; background: #eef6f4; }

.floating-card {
  border-color: #dcece9;
  background: rgba(255, 255, 255, 0.9);
  box-shadow: 0 14px 35px rgba(15, 118, 110, 0.09);
}

.floating-card > span:first-child { background: linear-gradient(135deg, #12b8a6, #07947f); }

.section-number { color: rgba(15, 143, 131, 0.075); }
.section-tint {
  border-color: rgba(15, 143, 131, 0.1);
  background:
    radial-gradient(circle at 98% 12%, rgba(216, 247, 240, 0.24), transparent 24rem),
    #f8fbfa;
}

.reading-card,
.code-explanation,
.panel-card,
.lesson-notes article,
.layout-guide-grid article,
.method-card,
.principle-cards article,
.breakpoint-list article,
.case-brief,
.lesson-sidebar,
.lesson-viewport {
  border-color: rgba(15, 143, 131, 0.12);
  background-color: rgba(255, 255, 255, 0.82);
  box-shadow: 0 12px 34px rgba(15, 118, 110, 0.06);
}

.reading-card-primary {
  background:
    radial-gradient(circle at 100% 0%, rgba(216, 247, 240, 0.3), transparent 14rem),
    rgba(255, 255, 255, 0.86);
}

.key-callout,
.case-step,
.theory-band article,
.theory-pair > div {
  border-color: rgba(15, 143, 131, 0.12);
  background: #f0fdfa;
}

.course-workspace { background: #f3f9f7; }
.lesson-sidebar {
  background:
    radial-gradient(circle at 15% 0%, rgba(216, 247, 240, 0.28), transparent 11rem),
    rgba(255, 255, 255, 0.88);
}

.lesson-menu button:hover,
.lesson-toolbar button:hover { border-color: rgba(15, 143, 131, 0.18); background: #f0fdfa; }
.lesson-menu button.active { border-color: rgba(15, 143, 131, 0.15); background: #eaf9f6; }
.lesson-toolbar,
.lesson-pagination { border-color: rgba(15, 143, 131, 0.12); background: rgba(255, 255, 255, 0.9); }

.layout-stage,
.demo-lab,
.grid-lab,
.responsive-lab,
.semantic-inspector,
.principle-demo {
  border-color: rgba(15, 143, 131, 0.12);
  background-color: rgba(255, 255, 255, 0.82);
  box-shadow: 0 16px 42px rgba(15, 118, 110, 0.07);
}

.flex-item.item-a { background: #14b8a6; }
.flex-item.item-b { background: #0f9f91; }
.flex-item.item-c { background: #087f76; }

.grid-canvas article {
  border-color: rgba(15, 143, 131, 0.17);
  color: #0f8f83;
  background: linear-gradient(145deg, #e3f8f4, #f0fdfa);
}

.grid-canvas article:nth-child(3n + 2) {
  color: #0f8f83;
  background: linear-gradient(145deg, #ccfbf1, #e9faf6);
}

.grid-canvas article:nth-child(3n) {
  color: #087f76;
  background: linear-gradient(145deg, #d9f5ef, #f0fdfa);
}

.viewport-page header { background: #e3f8f4; }
.viewport-page header b,
.vp-copy small,
.vp-copy button { background: #14b8a6; }

.summary-card {
  background:
    radial-gradient(circle at 10% 120%, rgba(189, 239, 230, 0.25), transparent 25rem),
    radial-gradient(circle at 90% -20%, rgba(216, 247, 240, 0.2), transparent 24rem),
    linear-gradient(125deg, #0f8f83, #0a8a7f 62%, #087f76);
  box-shadow: 0 20px 50px rgba(15, 118, 110, 0.1);
}

.summary-heading > span { color: #ccfbf1; }
.button-light { color: #0f8f83; box-shadow: 0 12px 30px rgba(15, 118, 110, 0.1); }
.back-to-top { background: linear-gradient(135deg, #12b8a6, #07947f); box-shadow: 0 12px 30px rgba(15, 118, 110, 0.12); }

/* ========================================================================== 
   VISUAL LAB — DARK EDITORIAL COURSE SYSTEM
   These rules are the visual baseline for Chapter 01 and future chapters.
   ========================================================================== */

:root {
  color-scheme: dark;
  --color-primary: var(--accent);
  --color-secondary: var(--accent-secondary);
  --color-purple: var(--accent-secondary);
  --color-blue-soft: var(--surface-secondary);
  --color-bg: var(--bg);
  --color-surface: var(--surface);
  --color-cream: var(--bg);
  --color-ink: var(--text-primary);
  --color-text: var(--text-primary);
  --color-muted: var(--text-secondary);
  --color-line: var(--border);
  --color-line-strong: var(--divider);
  --gradient-brand: var(--accent);
  --gradient-frame: var(--bg);
  --gradient-text: var(--accent);
  --gradient-soft: var(--surface-secondary);
  --shadow-sm: none;
  --shadow-md: none;
  --shadow-blue: none;
}

body { color: var(--text-primary); background: var(--bg); }
.page-frame,
.page-shell,
.summary-section,
.chapter-navigation { background: var(--bg); box-shadow: none; }
.section-tint,
.lesson-pages > .course-page.section-tint {
  border-color: var(--border);
  background: var(--bg);
}
.navbar { color: var(--text-primary); background: transparent; box-shadow: none; }
.gradient-text { color: var(--accent); background: none; -webkit-background-clip: initial; background-clip: initial; }
.chapter-pill,
.language-switch button.active { box-shadow: none; }
.button-primary { color: var(--bg); border-color: var(--accent); background: var(--accent); box-shadow: none; }
.button-primary:hover { color: var(--bg); background: var(--accent-secondary); box-shadow: none; }
.button-secondary { color: var(--text-primary); border-color: var(--divider); background: transparent; box-shadow: none; }
.button-secondary:hover { border-color: rgba(255, 255, 255, 0.34); background: var(--surface); }

/* Chapter cover */
.hero {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: 0;
  min-height: calc(100svh - 78px);
  padding: 0;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
}

.hero-copy {
  grid-column: 1 / span 6;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: flex-start;
  padding: clamp(5rem, 8vw, 8rem) var(--page-gutter) 4rem;
}

.chapter-kicker {
  display: grid;
  grid-template-columns: auto 44px auto;
  align-items: center;
  gap: 0.9rem;
  margin-bottom: clamp(3.5rem, 6vw, 6rem);
  color: var(--text-secondary);
  font-size: 0.62rem;
  font-weight: 620;
  letter-spacing: 0.18em;
}

.chapter-kicker i { width: 44px; height: 1px; border-radius: 0; background: var(--text-muted); }

.hero h1 {
  margin-bottom: 2rem;
  font-size: clamp(4rem, 6.6vw, 7.1rem);
  font-weight: 570;
  line-height: 0.94;
  letter-spacing: -0.075em;
}

.hero-copy > p {
  max-width: 620px;
  margin-bottom: 2.25rem;
  color: var(--text-secondary);
  font-size: 0.94rem;
  line-height: 1.9;
}

.hero-actions { display: flex; flex-wrap: wrap; gap: 0.85rem; margin-bottom: 2.8rem; }
.hero-meta {
  display: grid;
  grid-template-columns: repeat(3, auto);
  gap: 0;
  padding-top: 1.2rem;
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.68rem;
}
.hero-meta span { display: flex; align-items: baseline; gap: 0.45rem; min-width: 130px; padding-right: 1.3rem; }
.hero-meta span + span { padding-left: 1.3rem; border-left: 1px solid var(--border); }
.hero-meta b { color: var(--text-primary); font-size: 1.18rem; font-weight: 550; }

.hero-visual {
  position: relative;
  grid-column: 7 / -1;
  min-height: calc(100svh - 78px);
  margin: 0;
  overflow: hidden;
  border-left: 1px solid var(--border);
  background: var(--surface);
}

.hero-visual::after {
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, rgba(17, 19, 17, 0.18), transparent 35%, rgba(17, 19, 17, 0.12));
  content: "";
}

.hero-visual > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: 63% center;
  filter: saturate(0.62) contrast(1.04) brightness(0.78);
}

.hero-visual figcaption {
  position: absolute;
  z-index: 2;
  inset: 0;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  align-items: flex-end;
  padding: clamp(2rem, 5vw, 5rem);
}

.hero-visual figcaption > span {
  margin-top: 30%;
  color: var(--text-primary);
  font-size: 0.7rem;
  line-height: 1.8;
  letter-spacing: 0.18em;
}

.chapter-image-index { display: flex; align-items: center; gap: 0.75rem; color: rgba(255, 255, 255, 0.48); font-size: 0.7rem; }
.chapter-image-index b { color: var(--text-primary); font-size: 0.82rem; font-weight: 560; }
.chapter-image-index i { width: 32px; height: 1px; background: rgba(255, 255, 255, 0.3); }
.chapter-image-index i:first-of-type { background: var(--accent); }

.learning-strip {
  display: grid;
  grid-template-columns: auto repeat(7, auto);
  justify-content: center;
  align-items: center;
  gap: clamp(0.7rem, 2.2vw, 2.2rem);
  min-height: 82px;
  padding: 1rem var(--page-gutter);
  border-top: 0;
  border-bottom: 1px solid var(--border);
  color: var(--text-muted);
  background: var(--bg-alt);
  font-size: 0.68rem;
}
.learning-strip > span { color: var(--accent-secondary); font-weight: 620; letter-spacing: 0.18em; }
.learning-strip div { display: flex; align-items: center; gap: 0.55rem; white-space: nowrap; }
.learning-strip i { display: inline; width: auto; height: auto; color: var(--accent); background: none; font-size: 0.62rem; }
.learning-strip b { color: var(--text-muted); font-weight: 400; }

/* Study workspace: table of contents / lesson / context */
.course-workspace { background: var(--bg-alt); }

body.study-mode { min-height: 100dvh; overflow: hidden; }
body.study-mode .page-frame { width: 100%; height: 100dvh; margin: 0; }
body.study-mode .page-shell { display: grid; grid-template-rows: 78px minmax(0, 1fr); height: 100%; }
body.study-mode .hero,
body.study-mode .learning-strip,
body.study-mode .site-footer,
body.study-mode .scroll-progress,
body.study-mode .back-to-top { display: none; }

body.study-mode .course-workspace {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr) 188px;
  gap: 0;
  height: 100%;
  padding: 0;
  border-top: 1px solid var(--border);
  background: var(--bg);
}

.lesson-sidebar {
  display: grid;
  grid-template-rows: auto minmax(0, 1fr) auto;
  min-height: 0;
  padding: 2rem 1.25rem 1.25rem;
  overflow: hidden;
  border: 0;
  border-right: 1px solid var(--border);
  border-radius: 0;
  background: var(--bg-alt);
  box-shadow: none;
}

.sidebar-heading { padding: 0 0 1.5rem; }
.sidebar-heading > span { color: var(--accent-secondary); font-size: 0.55rem; font-weight: 620; letter-spacing: 0.16em; }
.sidebar-heading h2 { margin: 0.65rem 0 0.8rem; color: var(--text-primary); font-size: 1.22rem; font-weight: 560; line-height: 1.25; }
.sidebar-heading p { margin: 0; color: var(--text-muted); font-size: 0.5rem; letter-spacing: 0.16em; }

.lesson-menu { gap: 0; padding: 0; scrollbar-color: var(--accent-dark) transparent; }
.lesson-menu button {
  grid-template-columns: 28px minmax(0, 1fr) auto;
  gap: 0.55rem;
  min-height: 50px;
  padding: 0.45rem 0;
  border: 0;
  border-bottom: 1px solid var(--border);
  border-radius: 0;
  color: var(--text-secondary);
  background: transparent;
  transition: color 180ms ease, transform 180ms var(--ease);
}
.lesson-menu button:hover { color: var(--text-primary); background: transparent; transform: translateX(2px); }
.lesson-menu button > span {
  display: block;
  width: auto;
  height: auto;
  color: var(--text-muted);
  background: none;
  font-size: 0.55rem;
  letter-spacing: 0.08em;
}
.lesson-menu button > div { gap: 0.12rem; }
.lesson-menu button b { font-size: 0.69rem; font-weight: 540; }
.lesson-menu button small { color: var(--text-muted); font-size: 0.47rem; letter-spacing: 0.04em; }
.lesson-menu button > i { color: var(--accent); }
.lesson-menu button.active { border-color: var(--divider); color: var(--accent); background: transparent; }
.lesson-menu button.active > span { color: var(--accent); background: none; box-shadow: none; }

.sidebar-progress { padding: 1rem 0 0; }
.sidebar-progress > div:first-child { color: var(--text-muted); font-size: 0.54rem; }
.sidebar-progress strong { color: var(--accent); }
.sidebar-progress > div:last-child { height: 2px; border-radius: 0; background: var(--surface-secondary); }
.sidebar-progress i { height: 100%; border-radius: 0; background: var(--accent); }

.lesson-viewport {
  display: grid;
  grid-template-rows: 64px minmax(0, 1fr) 64px;
  min-width: 0;
  min-height: 0;
  overflow: hidden;
  border: 0;
  border-right: 1px solid var(--border);
  border-radius: 0;
  background: var(--bg);
  box-shadow: none;
}

.lesson-toolbar {
  padding: 0 clamp(1.25rem, 3vw, 2.5rem);
  border-bottom: 1px solid var(--border);
  background: var(--bg);
}
.lesson-toolbar > div { gap: 0.75rem; }
.lesson-toolbar span { color: var(--accent-secondary); font-size: 0.53rem; font-weight: 620; letter-spacing: 0.14em; }
.lesson-toolbar strong { font-size: 0.76rem; font-weight: 540; }
.lesson-toolbar > button {
  min-height: 34px;
  padding: 0 0.7rem;
  border: 0;
  border-radius: 0;
  color: var(--text-muted);
  background: transparent;
}
.lesson-toolbar > button:hover { color: var(--accent); background: transparent; }

.lesson-toolbar .lesson-mode-tabs {
  gap: 0;
  padding: 0;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
}
.lesson-toolbar .lesson-mode-tabs button {
  min-height: 32px;
  padding: 0 0.85rem;
  border-radius: 5px;
  color: var(--text-muted);
  background: transparent;
  font-size: 0.59rem;
}
.lesson-toolbar .lesson-mode-tabs button:hover { color: var(--text-primary); background: var(--surface-secondary); }
.lesson-toolbar .lesson-mode-tabs button.active { color: var(--bg); background: var(--accent); box-shadow: none; }

.lesson-pages { background: var(--bg); }
.lesson-pages > .course-page {
  height: 100%;
  padding: clamp(2rem, 4vw, 4rem);
  scrollbar-color: var(--accent-dark) transparent;
}
.lesson-pages > .course-page.active { animation: editorial-enter 260ms var(--ease) both; }
@keyframes editorial-enter { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: translateY(0); } }
.lesson-pages > .course-page > * { width: min(100%, 980px); margin-right: auto; margin-left: auto; }

.course-workspace .section-heading { gap: 2.5rem; margin-bottom: 3rem; }
.course-workspace .section-number { position: static; margin-bottom: 1rem; color: var(--accent); font-size: 0.58rem; letter-spacing: 0.15em; }
.course-workspace .section-heading h2 { color: var(--text-primary); font-size: clamp(2.3rem, 4vw, 4.2rem); font-weight: 570; }
.course-workspace .section-intro { max-width: 600px; color: var(--text-secondary); font-size: 0.82rem; line-height: 1.85; }

.lesson-context {
  display: flex;
  min-width: 0;
  padding: 2rem 1.25rem;
  flex-direction: column;
  color: var(--text-muted);
  background: var(--bg-alt);
}
.lesson-context > div + div { margin-top: 3rem; }
.lesson-context span { color: var(--text-muted); font-size: 0.49rem; font-weight: 620; letter-spacing: 0.16em; }
.lesson-context strong { display: block; margin: 0.65rem 0 0.8rem; color: var(--text-primary); font-size: 0.86rem; font-weight: 540; }
.lesson-context > div:first-child > i { display: block; height: 2px; background: var(--surface-secondary); }
.lesson-context > div:first-child > i b { display: block; width: 11.111%; height: 100%; background: var(--accent); transition: width 240ms var(--ease); }
.lesson-context p { margin: 0; padding: 0.7rem 0; border-bottom: 1px solid var(--border); color: var(--text-secondary); font-size: 0.59rem; line-height: 1.35; }
.lesson-context small { margin-top: auto; color: var(--text-muted); font-size: 0.52rem; line-height: 1.7; }

.lesson-pagination {
  padding: 0 clamp(1.25rem, 3vw, 2.5rem);
  border-top: 1px solid var(--border);
  background: var(--bg);
}
.lesson-pagination > button { border-radius: 4px; color: var(--text-secondary); background: transparent; }
.lesson-pagination > button:hover:not(:disabled) { color: var(--accent); background: transparent; }
.lesson-pagination small { color: var(--text-muted); }
.lesson-pagination > div { color: var(--text-muted); }
.lesson-pagination > div > i { height: 2px; border-radius: 0; background: var(--surface-secondary); }
.lesson-pagination > div > i b { border-radius: 0; background: var(--accent); }

/* Editorial learning content */
.study-panel.active { animation: editorial-enter 220ms var(--ease) both; }
.course-workspace h3,
.course-workspace h4 { color: var(--text-primary); font-weight: 560; }
.course-workspace p { color: var(--text-secondary); }

.case-step {
  grid-template-columns: 170px 1fr;
  gap: 1rem;
  margin: 0 auto 2.5rem;
  padding: 1.1rem 0;
  border: 0;
  border-top: 1px solid var(--divider);
  border-bottom: 1px solid var(--border);
  border-radius: 0;
  background: transparent;
}
.case-step > span { padding: 0; color: var(--accent-secondary); background: none; font-size: 0.52rem; font-weight: 620; letter-spacing: 0.13em; }
.case-step > div { gap: 0.8rem; }
.case-step b { color: var(--text-primary); font-size: 0.66rem; font-weight: 560; }
.case-step p { color: var(--text-secondary); font-size: 0.68rem; }

.case-brief {
  display: grid;
  grid-template-columns: 1.1fr 0.95fr 0.95fr;
  gap: 0;
  margin-bottom: 3rem;
  padding: 0;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  box-shadow: none;
}
.case-brief > div,
.case-brief article { padding: 1.35rem; border-radius: 0; background: transparent; }
.case-brief > div { color: var(--text-primary); border-right: 1px solid var(--border); background: var(--surface-secondary); }
.case-brief article + article { border-left: 1px solid var(--border); }
.case-brief span { color: var(--accent-secondary); }
.case-brief h3 { font-size: 0.95rem; font-weight: 560; }
.case-brief article b { color: var(--accent); font-size: 0.62rem; font-weight: 600; }
.case-brief article p { color: var(--text-secondary); }

.reading-card {
  padding: clamp(1.5rem, 2.8vw, 2.6rem);
  border: 0;
  border-left: 2px solid var(--accent);
  border-radius: 0;
  background: var(--surface);
  box-shadow: none;
}
.reading-card-primary { background: var(--surface); }
.reading-kicker,
.code-explanation > span { color: var(--accent-secondary); font-weight: 620; letter-spacing: 0.17em; }
.reading-card h3,
.code-explanation h3 { font-weight: 560; }
.reading-card > p { max-width: var(--reading-width); color: var(--text-secondary); font-size: 0.78rem; line-height: 1.9; }
.reading-card strong { color: var(--text-primary); }

.theory-pair { gap: 0; margin: 1.5rem 0; border-top: 1px solid var(--border); border-bottom: 1px solid var(--border); }
.theory-pair > div { padding: 1.15rem 0; border: 0; border-radius: 0; background: transparent; }
.theory-pair > div + div { padding-left: 1.2rem; border-left: 1px solid var(--border); }

.key-callout {
  grid-template-columns: 150px 1fr;
  margin-top: 1.5rem;
  padding: 1.1rem 0;
  border: 0;
  border-top: 1px solid var(--divider);
  border-radius: 0;
  color: var(--text-secondary);
  background: transparent;
}
.key-callout b { color: var(--accent); font-weight: 620; }
.key-callout.warning { border-color: var(--divider); background: transparent; }
.key-callout.warning b { color: var(--accent-secondary); }

.lesson-notes { gap: 0; margin-top: 1.5rem; border-top: 1px solid var(--border); }
.lesson-notes article { padding: 1.2rem 1rem 0 0; border: 0; border-radius: 0; background: transparent; box-shadow: none; }
.lesson-notes article + article { padding-left: 1rem; border-left: 1px solid var(--border); }
.lesson-notes article::before,
.lesson-notes article.pitfall::before { color: var(--accent-secondary); }
.lesson-notes p { color: var(--text-secondary); }

.region-list article,
.semantic-list article,
.layout-guide-grid article,
.breakpoint-list article {
  border: 0;
  border-bottom: 1px solid var(--border);
  border-radius: 0;
  color: var(--text-primary);
  background: transparent;
  box-shadow: none;
}
.region-list article:hover,
.semantic-list article:hover { border-color: var(--divider); box-shadow: none; transform: translateY(-2px); }
.region-list article > span { color: var(--accent); background: var(--surface-secondary); }
.semantic-list code { color: var(--accent); }

.theory-band { gap: 0; border-top: 1px solid var(--border); }
.theory-band article { padding: 1.25rem; border: 0; border-right: 1px solid var(--border); border-radius: 0; background: transparent; }
.theory-band article:last-child { border-right: 0; }
.theory-band b { color: var(--accent); }

/* Code */
.lesson-code-card,
.code-card {
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-primary);
  background: var(--surface-deep);
  box-shadow: none;
}
.lesson-code-card > header,
.code-card-bar { border-bottom: 1px solid var(--border); background: #101210; }
.lesson-code-card > header > div,
.code-card-bar > span { display: none; }
.lesson-code-card > header span,
.code-card-bar small { color: var(--text-muted); font-family: var(--font-mono); letter-spacing: 0.06em; }
.lesson-code-card button,
.lesson-code-card .copy-tree,
.copy-tree { border-color: var(--border); border-radius: 4px; color: var(--text-secondary); background: transparent; }
.lesson-code-card button:hover,
.copy-tree:hover { color: var(--accent); background: var(--surface); }
.lesson-code-card pre,
.code-card pre { color: var(--text-secondary); font-family: var(--font-mono); line-height: 1.8; }
.code-card .tag,
.code-comment { color: var(--accent-secondary); }
.code-explanation { padding: 2rem; border: 1px solid var(--border); border-radius: 8px; background: var(--surface); }
.code-explanation li { border-radius: 0; color: var(--text-secondary); background: transparent; }
.code-explanation li + li { border-top: 1px solid var(--border); }
.code-explanation li::before { color: var(--accent); background: transparent; }

/* Comparisons and experiments */
.layout-option,
.method-card,
.principle-cards article {
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-primary);
  background: var(--surface);
  box-shadow: none;
}
.layout-option:hover,
.method-card:hover,
.principle-cards article:hover { border-color: var(--divider); box-shadow: none; transform: translateY(-2px); }
.layout-option.active { border-color: var(--accent-dark); box-shadow: inset 2px 0 0 var(--accent); }
.layout-option small,
.method-card > p,
.method-card > small,
.principle-cards p { color: var(--text-secondary); }
.mini-wire,
.layout-option.active .mini-wire { border-radius: 4px; background: var(--surface-deep); }
.mini-wire i,
.layout-option.active .mini-wire i { border-radius: 1px; background: var(--text-muted); }

.layout-stage,
.demo-lab,
.grid-lab,
.responsive-lab,
.semantic-inspector,
.principle-demo {
  overflow: hidden;
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-primary);
  background: var(--surface);
  box-shadow: none;
}

.stage-toolbar,
.grid-toolbar,
.responsive-topline { border-color: var(--border); }
.stage-toolbar > div { display: none; }
.live-dot,
.preview-label,
.grid-toolbar > div > small,
.responsive-topline span { color: var(--text-muted); }
.live-dot::before,
.preview-label i { background: var(--accent-secondary); }

.large-wireframe,
.semantic-canvas,
.method-demo-stage,
.principle-stage,
.viewport-track {
  border-color: var(--border);
  border-radius: 6px;
  background: var(--surface-deep);
}
.wire-header,
.wire-footer { border-radius: 3px; background: #2a2e2a; }
.wire-header i { border-radius: 3px; background: var(--accent-dark); }
.wire-header span,
.wire-header b { background: #555b55; }
.wire-content article { border-color: var(--border); border-radius: 4px; background: var(--surface-secondary); }
.wire-content article i { border-radius: 3px; background: #303630; }
.wire-content article h4 { background: var(--accent-dark); }
.wire-content article p { background: #555b55; }
.layout-cards .wire-content article { box-shadow: none; }
.stage-caption small { color: var(--text-muted); }
.stage-caption p { color: var(--text-secondary); }

.method-card.featured { color: var(--text-primary); border-color: var(--accent-dark); background: var(--surface-secondary); box-shadow: none; }
.method-top span,
.featured .method-top span { color: var(--accent); background: var(--surface-deep); }
.method-top code,
.featured .method-top code { color: var(--text-muted); }
.featured > p,
.featured > small { color: var(--text-secondary); }
.method-visual,
.flex-visual { border-radius: 5px; background: var(--surface-deep); }
.method-visual i,
.flex-visual i { border-radius: 3px; color: var(--bg); background: var(--accent-secondary); }

.demo-controls { border-color: var(--border); background: var(--bg-alt); }
.control-title span { color: var(--accent-secondary); font-weight: 620; }
.demo-controls legend { color: var(--text-secondary); }
.demo-controls legend small { color: var(--text-muted); }
.segmented { border: 1px solid var(--border); border-radius: 6px; background: var(--surface-deep); }
.segmented button { border-radius: 4px; color: var(--text-muted); }
.segmented button:hover { color: var(--text-primary); }
.segmented button.active { color: var(--bg); background: var(--accent); box-shadow: none; }
.code-output,
.grid-toolbar > code { border: 1px solid var(--border); border-radius: 6px; color: var(--text-muted); background: var(--surface-deep); }
.code-output code,
.grid-toolbar > code { color: var(--accent-secondary); }

.flex-canvas,
.grid-canvas {
  border-color: var(--divider);
  border-radius: 6px;
  background:
    linear-gradient(rgba(255, 255, 255, 0.045) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.045) 1px, transparent 1px),
    var(--surface-deep);
  background-size: 28px 28px;
}
.flex-item {
  border-color: rgba(255, 255, 255, 0.14);
  border-radius: 6px;
  color: var(--bg);
  box-shadow: none;
}
.flex-item.item-a { background: var(--accent); }
.flex-item.item-b { color: var(--text-primary); background: var(--accent-dark); }
.flex-item.item-c { color: var(--text-primary); background: #747b72; }
.flex-item:hover { transform: translateY(-2px); }
.axis-label { color: var(--text-muted); }
.axis-main i,
.axis-cross i { background: #555a55; }

.grid-presets button { border-color: var(--border); border-radius: 5px; color: var(--text-secondary); background: transparent; }
.grid-presets button:hover,
.grid-presets button.active { border-color: var(--accent); color: var(--bg); background: var(--accent); }
.grid-canvas article,
.grid-canvas article:nth-child(3n + 2),
.grid-canvas article:nth-child(3n) {
  border-color: rgba(220, 235, 207, 0.22);
  border-radius: 5px;
  color: var(--text-primary);
  background: #303630;
  box-shadow: none;
}
.grid-canvas article:nth-child(3n + 2) { background: #252a25; }
.grid-canvas article:nth-child(3n) { color: var(--bg); background: var(--accent-secondary); }
.grid-canvas article span,
.grid-canvas article small { color: var(--text-muted); }
.grid-canvas article:nth-child(3n) span,
.grid-canvas article:nth-child(3n) small { color: var(--accent-dark); }
.grid-note > span { color: var(--bg); background: var(--accent); }

.principle-cards article > span { color: var(--accent); background: var(--surface-deep); }
.principle-icon { background: var(--surface-deep); }
.align-icon i,
.spacing-icon i { background: var(--accent-dark); }
.align-icon::before { background: var(--accent); }
.hierarchy-icon { color: var(--accent-secondary); }
.consistency-icon i { border-color: var(--accent-dark); background: var(--surface); }

.responsive-workspace,
.viewport-shell,
.viewport-browser { border-color: var(--border); background: var(--surface); }
.device { color: var(--text-muted); }
.device.active { color: var(--accent); }
.responsive-topline code { color: var(--accent); background: var(--surface-deep); }
.viewport-page { background: var(--surface-deep); }
.viewport-page header { background: #2a2e2a; }
.viewport-page header b,
.vp-copy small,
.vp-copy button { background: var(--accent-dark); }
.viewport-page header nav i,
.vp-copy p { background: #555a55; }
.vp-copy h4 { background: var(--text-secondary); }
.vp-image { border-radius: 4px; background: #303630; }
.viewport-page section article { border-color: var(--border); border-radius: 4px; background: var(--surface-secondary); }
.range-wrap input { accent-color: var(--accent); }
.range-wrap input::-webkit-slider-thumb { border-color: var(--bg); background: var(--accent); box-shadow: none; }

.anatomy-diagram,
.semantic-canvas { border-color: var(--border); background: var(--surface-deep); }
.anatomy-header,
.anatomy-nav,
.anatomy-main,
.anatomy-side,
.anatomy-footer,
[data-semantic-region] { border-color: var(--border); color: var(--text-secondary); background: var(--surface-secondary); }
.journey-active,
[data-semantic-region].active { border-color: var(--accent-dark); color: var(--accent); background: #252a25; }
.semantic-buttons button,
.method-demo-controls button,
.principle-demo-controls button { border-color: var(--border); border-radius: 5px; color: var(--text-secondary); background: transparent; }
.semantic-buttons button:hover,
.semantic-buttons button.active,
.method-demo-controls button:hover,
.method-demo-controls button.active,
.principle-demo-controls button:hover,
.principle-demo-controls button.active { border-color: var(--accent); color: var(--bg); background: var(--accent); }
.semantic-result,
.method-demo-result,
.journey-result { border-color: var(--border); color: var(--text-secondary); background: var(--surface-deep); }

/* Summary */
.course-workspace .summary-section { background: var(--bg); }
.summary-card,
.course-workspace .summary-card {
  border: 1px solid var(--divider);
  border-radius: 8px;
  color: var(--text-primary);
  background: var(--surface);
  box-shadow: none;
}
.summary-heading > span { color: var(--accent-secondary); }
.summary-heading p { color: var(--text-secondary); }
.checklist span { color: var(--bg); background: var(--accent); }
.button-light { color: var(--bg); background: var(--text-primary); box-shadow: none; }
.summary-orb { display: none; }
.summary-chapter-links { border-color: var(--border); }
.summary-chapter-links button { border-color: var(--border); border-radius: 5px; color: var(--text-secondary); background: transparent; }
.summary-chapter-links button:hover:not(:disabled) { color: var(--bg); background: var(--accent); }
.summary-chapter-links small { color: var(--text-muted); }
.back-to-top { color: var(--text-primary); background: var(--surface); box-shadow: none; }

@media (max-width: 1220px) {
  body.study-mode .course-workspace { grid-template-columns: 210px minmax(0, 1fr); }
  .lesson-context { display: none; }
}

@media (max-width: 960px) {
  .hero { display: flex; flex-direction: column; }
  .hero-copy { padding-top: 6rem; padding-bottom: 4rem; }
  .hero-visual { min-height: 560px; border-top: 1px solid var(--border); border-left: 0; }
  .hero-visual > img { position: absolute; inset: 0; }
  .hero-visual figcaption { padding: 2rem var(--page-gutter); }
  .hero-visual figcaption > span { margin-top: 0; }

  body.study-mode .page-shell { grid-template-rows: 68px minmax(0, 1fr); }
  body.study-mode .course-workspace { grid-template-columns: 1fr; grid-template-rows: auto minmax(0, 1fr); }
  .lesson-sidebar { display: block; padding: 0.55rem var(--page-gutter); border-right: 0; border-bottom: 1px solid var(--border); }
  .sidebar-heading,
  .sidebar-progress { display: none; }
  .lesson-menu { display: flex; gap: 1.2rem; overflow-x: auto; }
  .lesson-menu button { grid-template-columns: auto auto; flex: 0 0 auto; width: auto; border-bottom: 0; }
  .lesson-menu button small,
  .lesson-menu button > i { display: none; }
  .lesson-viewport { border-right: 0; }
}

@media (max-width: 700px) {
  .hero-copy { padding-top: 4.5rem; }
  .chapter-kicker { margin-bottom: 3.5rem; }
  .hero h1 { font-size: clamp(3.5rem, 16vw, 5rem); }
  .hero-meta { width: 100%; }
  .hero-meta span { min-width: 0; padding-right: 0.75rem; }
  .hero-meta span + span { padding-left: 0.75rem; }
  .hero-visual { min-height: 470px; }
  .hero-visual figcaption > span { font-size: 0.6rem; }
  .chapter-image-index i { width: 22px; }
  .learning-strip { display: flex; justify-content: flex-start; overflow-x: auto; }

  .course-workspace .section-heading { grid-template-columns: 1fr; gap: 1.3rem; }
  .lesson-toolbar-title { display: none !important; }
  .lesson-toolbar { padding: 0 0.8rem; }
  .lesson-pages > .course-page { padding: 2rem 1.1rem; }
  .lesson-pagination { padding: 0 0.8rem; }
  .lesson-pagination button span { display: none; }

  .theory-grid,
  .axis-theory,
  .code-lesson-grid,
  .layout-switcher,
  .method-cards,
  .demo-lab,
  .case-brief,
  .principle-cards,
  .responsive-workspace { grid-template-columns: 1fr; }
  .case-brief > div { border-right: 0; border-bottom: 1px solid var(--border); }
  .case-brief article + article { border-left: 0; border-top: 1px solid var(--border); }
  .demo-controls { border-right: 0; border-bottom: 1px solid var(--border); }
  .layout-options { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .layout-option { grid-template-columns: 48px 1fr; }
  .mini-wire { width: 48px; }
  .lesson-notes { grid-template-columns: 1fr; }
  .lesson-notes article + article { padding-left: 0; border-left: 0; border-top: 1px solid var(--border); }
  .theory-pair { grid-template-columns: 1fr; }
  .theory-pair > div + div { padding-left: 0; border-left: 0; border-top: 1px solid var(--border); }
  .key-callout,
  .case-step { grid-template-columns: 1fr; }
}

@media (max-width: 480px) {
  body.study-mode .page-frame { height: 100dvh; margin: 0; padding: 0; }
  body.study-mode .site-header { padding: 0; }
  body.study-mode .navbar { min-height: 60px; }
  body.study-mode .page-shell { grid-template-rows: 60px minmax(0, 1fr); }
  .hero-actions { width: 100%; }
  .hero-actions .button { flex: 1; }
  .layout-options { grid-template-columns: 1fr; }
  .grid-toolbar { align-items: stretch; flex-direction: column; }
  .grid-toolbar > code { white-space: normal; }
  .flex-canvas { height: 330px; padding: 2.5rem 1.5rem; }
  .flex-item { flex-basis: 62px; height: 62px; }
  .summary-chapter-links { grid-template-columns: 1fr 1fr; }
}