.lecture-page {
  min-height: 100vh;
  background: var(--bg-0);
  color: var(--tx-1);
}

.lecture-site-header {
  min-height: 64px;
  padding: 0 28px;
  border-bottom: 1px solid var(--line);
  background: var(--bg-1);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.lecture-brand {
  color: var(--tx-1);
  text-decoration: none;
  font: 700 18px/1 var(--font-display);
}

.lecture-brand span,
.lecture-eyebrow,
.lecture-block-label,
.lecture-section-number {
  color: var(--accent);
}

.lecture-header-links {
  display: flex;
  align-items: center;
  gap: 10px;
}

.lecture-shell {
  width: min(980px, calc(100% - 32px));
  margin: 0 auto;
  padding: 56px 0 96px;
}

.lecture-hero {
  padding: 24px 0 42px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 40px;
}

.lecture-eyebrow {
  font: 600 11px/1.4 var(--font-display);
  letter-spacing: .14em;
}

.lecture-hero h1 {
  max-width: 780px;
  margin: 14px 0;
  font: 600 clamp(34px, 6vw, 68px)/1.06 var(--font-display);
}

.lecture-summary {
  max-width: 720px;
  color: var(--tx-2);
  font-size: 16px;
  line-height: 1.8;
}

.lecture-meta {
  margin-top: 18px;
  color: var(--tx-3);
  font: 500 11px/1.6 var(--font-mono);
  letter-spacing: .06em;
}

.lecture-section {
  margin: 0 0 52px;
}

.lecture-section-heading {
  display: grid;
  grid-template-columns: 48px minmax(0, 1fr);
  align-items: baseline;
  gap: 12px;
  margin-bottom: 18px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--line);
}

.lecture-section-heading h2 {
  font: 600 25px/1.3 var(--font-display);
}

.lecture-section-number {
  font: 600 11px/1 var(--font-mono);
}

.lecture-block {
  margin: 0 0 14px;
  padding: 22px;
  border: 1px solid var(--line);
  background: var(--bg-1);
  color: var(--tx-1);
}

.lecture-block-text {
  white-space: pre-wrap;
  line-height: 1.85;
}

.lecture-block-label {
  display: block;
  margin-bottom: 10px;
  font: 600 11px/1.4 var(--font-display);
  letter-spacing: .1em;
  text-transform: uppercase;
}

.lecture-block-callout {
  border-left: 3px solid var(--accent);
  background: var(--accent-dim);
}

.lecture-block-callout[data-tone="warning"] {
  border-left-color: var(--err);
}

.lecture-block-example,
.lecture-block-question_ref {
  background: var(--bg-2);
}

.lecture-answer {
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px dashed var(--line-strong);
  color: var(--tx-2);
}

.lecture-answer[hidden] {
  display: none;
}

.lecture-analysis-label {
  display: block;
  margin-top: 14px;
}

.lecture-question-options {
  display: grid;
  gap: 8px;
  margin: 16px 0 0;
  padding: 0;
  list-style: none;
}

.lecture-question-options li {
  display: grid;
  grid-template-columns: 28px minmax(0, 1fr);
  align-items: start;
  gap: 6px;
  color: var(--tx-2);
}

.lecture-question-options .lecture-block-text {
  margin: 0;
}

.lecture-math-inline {
  display: inline-block;
  margin: 0 .08em;
  color: var(--tx-1);
}

.lecture-math-display {
  overflow-x: auto;
  padding: 10px 0;
  color: var(--tx-1);
  text-align: center;
}

.lecture-caption,
.lecture-empty,
.lecture-render-warning {
  color: var(--tx-3);
  line-height: 1.7;
}

.lecture-caption {
  margin-top: 10px;
  text-align: center;
  font-size: 12px;
}

.lecture-ref-code {
  display: inline-block;
  margin: 0 0 10px;
  color: var(--tx-3);
}

.lecture-knowledge-link {
  display: inline-block;
  margin-bottom: 8px;
  color: var(--tx-1);
  text-decoration-color: var(--accent);
}

.lecture-image {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 0 auto;
}

.lecture-catalog {
  display: grid;
  gap: 40px;
}

.lecture-course-group h2 {
  margin-bottom: 16px;
  font: 600 24px/1.3 var(--font-display);
}

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

.lecture-card {
  display: block;
  min-height: 170px;
  padding: 22px;
  border: 1px solid var(--line);
  background: var(--bg-1);
  color: var(--tx-1);
  text-decoration: none;
}

.lecture-card:hover {
  border-color: var(--accent);
  background: var(--accent-dim);
}

.lecture-card h3 {
  margin: 14px 0 10px;
  font-size: 19px;
}

.lecture-card p {
  color: var(--tx-2);
  line-height: 1.7;
}

.lecture-stage[hidden] {
  display: none;
}

.lecture-stage {
  position: fixed;
  inset: 0;
  z-index: 1000;
  display: grid;
  grid-template-rows: auto minmax(0, 1fr) auto;
  background: var(--bg-0);
}

.lecture-stage-header,
.lecture-stage-footer {
  padding: 18px 28px;
  border-bottom: 1px solid var(--line);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.lecture-stage-footer {
  border-top: 1px solid var(--line);
  border-bottom: 0;
}

.lecture-stage-content {
  width: min(1120px, calc(100% - 64px));
  margin: auto;
  overflow: auto;
  padding: 48px 0;
}

.lecture-stage-content h2 {
  margin-bottom: 28px;
  color: var(--tx-2);
  font: 500 20px/1.3 var(--font-display);
}

.lecture-stage-content .lecture-block {
  border: 0;
  background: transparent;
  font-size: clamp(20px, 3vw, 38px);
}

.lecture-stage-progress {
  color: var(--tx-3);
  font: 500 12px/1 var(--font-mono);
}

@media (max-width: 720px) {
  .lecture-site-header { padding: 14px 16px; }
  .lecture-card-grid { grid-template-columns: 1fr; }
  .lecture-shell { padding-top: 30px; }
  .lecture-stage-content { width: calc(100% - 32px); }
}