:root {
  --ls-bg: #eff5ff;
  --ls-bg-2: #f7faff;
  --ls-paper: rgba(255, 255, 255, 0.94);
  --ls-paper-strong: #ffffff;
  --ls-stage: #eef5ff;
  --ls-stage-grid: rgba(55, 118, 255, 0.14);
  --ls-ink: #17233f;
  --ls-muted: #66789a;
  --ls-line: rgba(121, 146, 196, 0.2);
  --ls-line-strong: rgba(81, 120, 204, 0.28);
  --ls-primary: #2f6df6;
  --ls-primary-strong: #1c57dc;
  --ls-primary-soft: rgba(47, 109, 246, 0.12);
  --ls-green: #19a974;
  --ls-orange: #f3a731;
  --ls-shadow-soft: 0 24px 60px rgba(46, 78, 147, 0.12);
  --ls-shadow-card: 0 20px 48px rgba(52, 85, 157, 0.1);
  color: var(--ls-ink);
  font-family: "Plus Jakarta Sans", "Noto Sans SC", "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at 15% 12%, rgba(113, 168, 255, 0.14), transparent 24%),
    radial-gradient(circle at 88% 10%, rgba(219, 236, 255, 0.9), transparent 30%),
    linear-gradient(180deg, var(--ls-bg-2), var(--ls-bg));
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background-image:
    linear-gradient(rgba(255, 255, 255, 0.38) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.38) 1px, transparent 1px);
  background-size: 32px 32px;
  opacity: 0.42;
}

a {
  color: inherit;
}

button,
input,
textarea,
select {
  font: inherit;
}

code {
  font-family: "JetBrains Mono", "Cascadia Code", monospace;
}

.lesson-page {
  position: relative;
  z-index: 1;
  width: min(1480px, calc(100% - 32px));
  margin: 0 auto;
  padding: 20px 0 28px;
}

.lesson-card {
  background: var(--ls-paper);
  border: 1px solid rgba(255, 255, 255, 0.72);
  border-radius: 28px;
  box-shadow: var(--ls-shadow-card);
  backdrop-filter: blur(14px);
}

.platform-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 18px 4px 24px;
}

.platform-brand,
.platform-user,
.platform-nav {
  display: flex;
  align-items: center;
}

.platform-brand {
  gap: 14px;
}

.platform-logo {
  position: relative;
  width: 56px;
  height: 56px;
  border-radius: 16px;
  background: linear-gradient(145deg, #5ea7ff, #255deb);
  box-shadow: 0 20px 36px rgba(47, 109, 246, 0.28);
  overflow: hidden;
}

.platform-logo span {
  position: absolute;
  inset: auto auto 12px 12px;
  width: 14px;
  height: 14px;
  border-radius: 4px;
  background: rgba(255, 255, 255, 0.92);
}

.platform-logo span:nth-child(2) {
  left: 28px;
  bottom: 12px;
  opacity: 0.72;
}

.platform-logo span:nth-child(3) {
  left: 20px;
  bottom: 28px;
  opacity: 0.84;
}

.platform-brand-copy {
  display: grid;
  gap: 4px;
}

.platform-brand-copy strong {
  font-size: 1.8rem;
  font-family: "Sora", "Noto Sans SC", sans-serif;
  letter-spacing: -0.04em;
}

.platform-brand-copy span {
  color: var(--ls-muted);
  font-size: 0.95rem;
}

.platform-nav {
  gap: 30px;
  justify-content: center;
  flex: 1;
}

.platform-nav-link {
  position: relative;
  padding: 14px 0;
  color: var(--ls-ink);
  text-decoration: none;
  font-weight: 600;
}

.platform-nav-link.is-active {
  color: var(--ls-primary);
}

.platform-nav-link.is-active::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: -10px;
  height: 4px;
  border-radius: 999px;
  background: linear-gradient(90deg, #69a3ff, #2f6df6);
}

.platform-user {
  gap: 12px;
}

.platform-icon-button,
.platform-avatar {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--ls-line);
  background: rgba(255, 255, 255, 0.82);
}

.platform-icon-button {
  cursor: pointer;
  color: var(--ls-muted);
}

.platform-avatar {
  font-weight: 700;
  color: var(--ls-primary);
  box-shadow: 0 14px 26px rgba(47, 109, 246, 0.12);
}

.lesson-hero {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: 22px;
  padding: 28px 30px;
  margin-bottom: 18px;
}

.lesson-hero-media {
  width: 90px;
  height: 90px;
  border-radius: 24px;
  background:
    radial-gradient(circle at 35% 30%, rgba(255, 255, 255, 0.88), transparent 24%),
    linear-gradient(145deg, rgba(78, 146, 255, 0.18), rgba(47, 109, 246, 0.08));
  display: grid;
  place-items: center;
}

.hero-model-badge {
  width: 60px;
  height: 60px;
  border-radius: 18px;
  background: linear-gradient(145deg, #68a7ff, #2f6df6);
  color: #fff;
  display: grid;
  place-items: center;
  font-weight: 800;
  font-size: 1.05rem;
  box-shadow: 0 18px 30px rgba(47, 109, 246, 0.22);
}

.lesson-hero-copy {
  display: grid;
  gap: 10px;
}

.hero-title-row {
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: wrap;
}

.hero-title-row h1 {
  margin: 0;
  font-size: clamp(2rem, 3.6vw, 3.5rem);
  line-height: 1.02;
  letter-spacing: -0.06em;
  font-family: "Sora", "Noto Sans SC", sans-serif;
}

.lesson-hero-copy p {
  margin: 0;
  color: var(--ls-muted);
  font-size: 1.02rem;
  max-width: 840px;
}

.review-badge,
.model-chip {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 34px;
  padding: 8px 14px;
  border-radius: 999px;
  background: rgba(92, 164, 255, 0.12);
  color: var(--ls-primary);
  border: 1px solid rgba(92, 164, 255, 0.2);
  font-size: 0.92rem;
  font-weight: 600;
}

.lesson-hero-actions,
.model-chip-row,
.import-actions,
.footer-tools,
.qa-score {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.hero-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 0 18px;
  border-radius: 18px;
  border: 1px solid var(--ls-line);
  background: rgba(255, 255, 255, 0.9);
  color: var(--ls-ink);
  text-decoration: none;
  cursor: pointer;
  transition: transform 140ms ease, box-shadow 140ms ease, border-color 140ms ease;
}

.hero-button:hover {
  transform: translateY(-1px);
  box-shadow: 0 14px 28px rgba(61, 97, 166, 0.12);
  border-color: var(--ls-line-strong);
}

.hero-button--primary {
  border-color: transparent;
  color: #fff;
  background: linear-gradient(135deg, var(--ls-primary), var(--ls-primary-strong));
  box-shadow: 0 18px 34px rgba(47, 109, 246, 0.28);
}

.hero-button--quiet {
  background: rgba(255, 255, 255, 0.72);
}

.workspace-grid {
  display: grid;
  grid-template-columns: 240px minmax(0, 1.55fr) 380px;
  gap: 18px;
  align-items: start;
}

.card-header {
  display: flex;
  align-items: start;
  justify-content: space-between;
  gap: 14px;
  margin-bottom: 16px;
}

.card-header h2 {
  margin: 0;
  font-size: 1.6rem;
  letter-spacing: -0.05em;
  font-family: "Sora", "Noto Sans SC", sans-serif;
}

.card-eyebrow {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  padding: 0 10px;
  border-radius: 999px;
  background: rgba(47, 109, 246, 0.08);
  color: var(--ls-primary);
  font-size: 0.76rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
}

.flow-sidebar,
.content-sidebar {
  padding: 22px;
}

.model-stage-card {
  padding: 22px;
}

.card-header--stage {
  margin-bottom: 18px;
}

.model-chip--interactive {
  background: rgba(25, 169, 116, 0.12);
  border-color: rgba(25, 169, 116, 0.18);
  color: #0e8d5f;
}

.stage-layout {
  display: grid;
  grid-template-columns: 68px minmax(0, 1fr);
  gap: 16px;
}

.tool-rail {
  display: grid;
  align-content: start;
  gap: 10px;
}

.tool-rail-button {
  min-height: 54px;
  border-radius: 18px;
  border: 1px solid var(--ls-line);
  background: rgba(255, 255, 255, 0.88);
  color: var(--ls-muted);
  cursor: pointer;
}

.viewer-panel {
  display: grid;
  gap: 16px;
}

.viewer-shell {
  position: relative;
  min-height: 560px;
  border-radius: 28px;
  overflow: hidden;
  background:
    radial-gradient(circle at 50% 18%, rgba(146, 192, 255, 0.26), transparent 26%),
    linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(237, 244, 255, 0.98));
  border: 1px solid rgba(157, 191, 255, 0.3);
}

#viewerCanvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  min-height: 560px;
  z-index: 2;
}

.viewer-grid-floor {
  position: absolute;
  inset: auto 0 0;
  height: 52%;
  z-index: 1;
  background-image:
    linear-gradient(rgba(47, 109, 246, 0.1) 1px, transparent 1px),
    linear-gradient(90deg, rgba(47, 109, 246, 0.1) 1px, transparent 1px);
  background-size: 42px 42px;
  mask-image: linear-gradient(180deg, transparent, rgba(0, 0, 0, 0.9) 16%, rgba(0, 0, 0, 0.98));
  transform: perspective(560px) rotateX(72deg);
  transform-origin: center top;
}

.viewer-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
  flex-wrap: wrap;
}

.viewer-helper {
  margin: 0;
  color: var(--ls-muted);
  font-size: 0.94rem;
}

.hotspot-layer {
  position: absolute;
  inset: 0;
  z-index: 3;
  pointer-events: none;
}

.hotspot-button {
  position: absolute;
  pointer-events: auto;
  border: 0;
  border-radius: 999px;
  padding: 10px 14px;
  background: rgba(255, 255, 255, 0.96);
  color: var(--ls-ink);
  box-shadow: 0 18px 36px rgba(47, 109, 246, 0.18);
  font-size: 0.82rem;
  font-weight: 700;
}

.hotspot-button.active {
  background: linear-gradient(135deg, var(--ls-primary), var(--ls-primary-strong));
  color: #fff;
}

.content-tabs {
  display: flex;
  gap: 18px;
  padding-bottom: 12px;
  border-bottom: 1px solid rgba(121, 146, 196, 0.16);
  margin-bottom: 18px;
  overflow-x: auto;
}

.content-tab {
  padding: 0 0 10px;
  border: 0;
  background: transparent;
  color: var(--ls-muted);
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
}

.content-tab.is-active {
  color: var(--ls-primary);
  box-shadow: inset 0 -3px 0 var(--ls-primary);
}

.content-block + .content-block {
  margin-top: 22px;
}

#objectives ul {
  margin: 0;
  padding-left: 20px;
  display: grid;
  gap: 10px;
}

#objectives li {
  color: var(--ls-ink);
  line-height: 1.65;
}

.teaching-note {
  margin-top: 22px;
  padding: 18px;
  border-radius: 22px;
  background: linear-gradient(135deg, rgba(47, 109, 246, 0.08), rgba(218, 233, 255, 0.84));
  border: 1px solid rgba(47, 109, 246, 0.12);
}

.teaching-note strong {
  display: block;
  margin-bottom: 8px;
  color: var(--ls-primary);
}

.teaching-note p {
  margin: 0;
  color: var(--ls-muted);
}

.section-nav {
  display: grid;
  gap: 14px;
  counter-reset: lesson-step;
}

.section-button {
  position: relative;
  display: grid;
  justify-items: start;
  gap: 6px;
  width: 100%;
  padding: 18px 18px 18px 68px;
  border: 1px solid rgba(121, 146, 196, 0.16);
  border-radius: 20px;
  background: rgba(255, 255, 255, 0.78);
  color: var(--ls-ink);
  text-align: left;
  cursor: pointer;
  transition: transform 140ms ease, border-color 140ms ease, box-shadow 140ms ease;
  counter-increment: lesson-step;
}

.section-button::before {
  content: counter(lesson-step);
  position: absolute;
  left: 18px;
  top: 18px;
  width: 34px;
  height: 34px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background: rgba(47, 109, 246, 0.1);
  color: var(--ls-primary);
  font-weight: 800;
}

.section-button::after {
  content: "";
  position: absolute;
  left: 34px;
  bottom: -14px;
  width: 2px;
  height: 14px;
  background: rgba(47, 109, 246, 0.16);
}

.section-button:last-child::after {
  display: none;
}

.section-button:hover,
.section-button.active {
  transform: translateY(-1px);
  border-color: rgba(47, 109, 246, 0.26);
  box-shadow: 0 16px 26px rgba(47, 109, 246, 0.1);
}

.section-button.active {
  background: linear-gradient(135deg, var(--ls-primary), var(--ls-primary-strong));
  color: #fff;
}

.section-button.active::before {
  background: rgba(255, 255, 255, 0.24);
  color: #fff;
}

.overview-hero {
  padding: 22px;
  border-radius: 24px;
  background:
    radial-gradient(circle at 88% 12%, rgba(140, 190, 255, 0.24), transparent 24%),
    linear-gradient(135deg, rgba(244, 248, 255, 0.98), rgba(234, 242, 255, 0.98));
  border: 1px solid rgba(47, 109, 246, 0.1);
  margin-bottom: 14px;
}

.overview-hero h3,
.active-section h3,
.structure-card h3 {
  margin: 8px 0 10px;
  font-size: 1.3rem;
  letter-spacing: -0.04em;
  font-family: "Sora", "Noto Sans SC", sans-serif;
}

.overview-hero p,
.overview-row p,
.overview-row strong,
.active-section p,
.structure-card p,
.question-list li {
  margin: 0;
  line-height: 1.7;
}

.overview-grid {
  display: grid;
  gap: 12px;
}

.overview-row {
  padding: 16px 18px;
  border-radius: 18px;
  background: rgba(246, 249, 255, 0.94);
  border: 1px solid rgba(47, 109, 246, 0.08);
}

.overview-label,
.section-kicker {
  display: inline-flex;
  color: var(--ls-primary);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.active-section {
  display: grid;
  gap: 16px;
}

.active-section-header {
  display: grid;
  gap: 8px;
}

.active-section-copy {
  padding: 18px 18px 0;
  border-radius: 20px;
  background: rgba(247, 250, 255, 0.92);
  border: 1px solid rgba(47, 109, 246, 0.08);
}

.fact-strip {
  padding: 14px 16px;
  border-radius: 18px;
  background: rgba(47, 109, 246, 0.08);
  color: var(--ls-primary-strong);
  border: 1px solid rgba(47, 109, 246, 0.08);
}

.key-point-list {
  display: grid;
  gap: 12px;
}

.key-point-row {
  padding: 16px 18px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.92);
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.key-point-row strong {
  display: block;
  margin-bottom: 8px;
  font-size: 1rem;
  line-height: 1.65;
}

.lesson-bottom-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.06fr) minmax(0, 1fr);
  gap: 18px;
  margin-top: 18px;
}

.knowledge-board,
.qa-board {
  padding: 22px;
}

#keyStructures {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.structure-card {
  padding: 18px;
  border-radius: 22px;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.96), rgba(243, 248, 255, 0.96));
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.structure-topline {
  display: flex;
  align-items: start;
  gap: 12px;
}

.structure-index {
  flex: none;
  width: 38px;
  height: 38px;
  border-radius: 14px;
  display: grid;
  place-items: center;
  background: rgba(47, 109, 246, 0.12);
  color: var(--ls-primary);
  font-size: 0.88rem;
  font-weight: 800;
}

.structure-role,
.structure-look-for {
  margin-top: 12px;
  display: grid;
  gap: 6px;
}

.qa-grid {
  display: grid;
  grid-template-columns: minmax(0, 0.96fr) minmax(0, 1.04fr);
  gap: 16px;
}

.question-bank {
  padding: 18px;
  border-radius: 22px;
  background: rgba(247, 250, 255, 0.96);
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.question-list {
  display: grid;
  gap: 12px;
  margin: 0;
  padding-left: 22px;
}

.question-list li::marker {
  color: var(--ls-primary);
  font-weight: 700;
}

#quizPanel {
  display: grid;
  gap: 14px;
}

.quiz-card {
  padding: 18px;
  border-radius: 22px;
  background: rgba(255, 255, 255, 0.96);
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.quiz-card--single,
.quiz-card--complete {
  min-height: 100%;
}

.quiz-card strong {
  display: block;
  margin-bottom: 14px;
  line-height: 1.6;
}

.quiz-progress {
  display: grid;
  gap: 10px;
  margin-bottom: 14px;
}

.quiz-progress-label {
  color: var(--ls-muted);
  font-size: 0.86rem;
  font-weight: 700;
}

.quiz-progress-bar {
  width: 100%;
  height: 8px;
  border-radius: 999px;
  background: rgba(121, 146, 196, 0.16);
  overflow: hidden;
}

.quiz-progress-bar span {
  display: block;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, #69a3ff, #2f6df6);
}

.quiz-state {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  padding: 0 10px;
  border-radius: 999px;
  background: rgba(47, 109, 246, 0.08);
  color: var(--ls-primary);
  font-size: 0.74rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 12px;
}

.quiz-options {
  display: grid;
  gap: 10px;
}

.quiz-option {
  width: 100%;
  padding: 14px 16px;
  border-radius: 16px;
  border: 1px solid rgba(121, 146, 196, 0.16);
  background: rgba(248, 251, 255, 0.94);
  color: var(--ls-ink);
  text-align: left;
  cursor: pointer;
}

.quiz-option.selected {
  border-color: rgba(47, 109, 246, 0.28);
  background: rgba(47, 109, 246, 0.08);
}

.quiz-option.correct {
  border-color: rgba(25, 169, 116, 0.32);
  background: rgba(25, 169, 116, 0.1);
}

.quiz-option.incorrect {
  border-color: rgba(243, 167, 49, 0.32);
  background: rgba(243, 167, 49, 0.12);
}

.quiz-option:disabled {
  cursor: not-allowed;
  opacity: 0.9;
}

.quiz-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 14px;
}

.quiz-action {
  min-height: 42px;
  padding: 0 14px;
  border-radius: 14px;
  border: 0;
  background: linear-gradient(135deg, var(--ls-primary), var(--ls-primary-strong));
  color: #fff;
  cursor: pointer;
}

.quiz-note {
  color: var(--ls-muted);
  font-size: 0.92rem;
}

.quiz-feedback {
  margin-top: 14px;
  padding: 14px 16px;
  border-radius: 18px;
  display: grid;
  gap: 6px;
}

.quiz-feedback p {
  margin: 0;
  color: inherit;
}

.quiz-feedback.muted {
  background: rgba(247, 250, 255, 0.98);
  color: var(--ls-muted);
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.quiz-feedback.success {
  background: rgba(25, 169, 116, 0.12);
  color: #0d8357;
}

.quiz-feedback.warning {
  background: rgba(243, 167, 49, 0.14);
  color: #8c6308;
}

.quiz-feedback.info {
  background: rgba(47, 109, 246, 0.1);
  color: var(--ls-primary-strong);
}

.lesson-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
  padding: 18px 22px;
  margin-top: 18px;
}

.footer-tools {
  color: var(--ls-muted);
  font-size: 0.92rem;
}

.footer-tools span:first-child {
  color: var(--ls-ink);
  font-weight: 700;
}

#attribution {
  margin: 0;
  color: var(--ls-muted);
  font-size: 0.88rem;
}

.model-import-panel {
  display: grid;
  gap: 16px;
  margin-top: 18px;
  padding: 18px;
  border-radius: 24px;
  background: linear-gradient(135deg, rgba(245, 249, 255, 0.98), rgba(234, 242, 255, 0.98));
  border: 1px solid rgba(47, 109, 246, 0.12);
}

.model-import-copy p,
.import-status {
  margin: 0;
  color: var(--ls-muted);
}

.dropzone {
  display: grid;
  justify-items: center;
  gap: 8px;
  padding: 28px 18px;
  border-radius: 22px;
  border: 1px dashed rgba(47, 109, 246, 0.32);
  background: rgba(255, 255, 255, 0.76);
  text-align: center;
  cursor: pointer;
}

.dropzone.dragging {
  background: rgba(47, 109, 246, 0.08);
  border-style: solid;
}

.dropzone strong {
  font-size: 1.04rem;
}

.import-status {
  padding: 14px 16px;
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.74);
  border: 1px solid rgba(121, 146, 196, 0.12);
}

.import-status.success {
  color: #0d8357;
  background: rgba(25, 169, 116, 0.12);
}

.import-status.error {
  color: #b04d2f;
  background: rgba(255, 126, 92, 0.12);
}

@media (max-width: 1280px) {
  .workspace-grid {
    grid-template-columns: 220px minmax(0, 1fr);
  }

  .content-sidebar {
    grid-column: 1 / -1;
  }

  .lesson-bottom-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 980px) {
  .lesson-page {
    width: min(100%, calc(100% - 20px));
  }

  .platform-header,
  .lesson-hero {
    grid-template-columns: 1fr;
  }

  .platform-header {
    display: grid;
    justify-items: start;
  }

  .platform-nav {
    width: 100%;
    justify-content: flex-start;
    overflow-x: auto;
  }

  .lesson-hero {
    display: grid;
    justify-items: start;
  }

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

  .stage-layout,
  .qa-grid,
  #keyStructures {
    grid-template-columns: 1fr;
  }

  .tool-rail {
    grid-auto-flow: column;
    grid-auto-columns: minmax(84px, 1fr);
    overflow-x: auto;
  }

  .viewer-shell,
  #viewerCanvas {
    min-height: 420px;
  }
}

@media (max-width: 640px) {
  .lesson-page {
    width: min(100%, calc(100% - 16px));
    padding-top: 14px;
  }

  .platform-brand-copy strong {
    font-size: 1.35rem;
  }

  .lesson-hero,
  .flow-sidebar,
  .model-stage-card,
  .content-sidebar,
  .knowledge-board,
  .qa-board,
  .lesson-footer {
    padding: 18px;
  }

  .hero-title-row h1 {
    font-size: 2rem;
  }

  .viewer-shell,
  #viewerCanvas {
    min-height: 340px;
  }

  .platform-nav {
    gap: 18px;
  }
}