/* ========== Design System: Historical Immersion ========== */
:root {
  /* Color Palette */
  --bg-deep: #1a1a2e;
  --bg-dark: #2d2d2d;
  --bg-card: #2a2a3e;
  --aged-paper: #f4e4bc;
  --muted-gold: #c9a227;
  --faded-blue: #4a6fa5;
  --cream: #faf3e0;
  --text-primary: #e8dcc8;
  --text-secondary: #b8a88a;
  --text-muted: #8a7d6a;
  --accent-red: #a63d40;
  --accent-green: #5d8a68;
  --border-subtle: rgba(201,162,39,0.2);
  --shadow-deep: rgba(0,0,0,0.4);
  --overlay-dark: rgba(26,26,46,0.85);
  --player-height: 64px;
  
  /* Typography */
  --font-heading: 'Special Elite', 'Courier Prime', monospace;
  --font-body-cn: 'Noto Serif SC', 'STSong', serif;
  --font-body-en: 'Georgia', 'Times New Roman', serif;
  --font-ui: 'Noto Sans SC', 'PingFang SC', sans-serif;
  --font-mono: 'Courier Prime', 'Courier New', monospace;
  
  /* Spacing Scale (4px base) */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;
  
  /* Border Radii */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  
  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-normal: 300ms ease;
  --transition-slow: 500ms ease;
}

/* ========== Reset & Base ========== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  font-size: 16px;
  overflow: hidden;
}

body {
  font-family: var(--font-body-cn);
  background: var(--bg-deep);
  color: var(--text-primary);
  line-height: 1.8;
  min-height: 100vh;
  overflow: hidden;
}

/* ========== Noise/Grain Texture Overlay ========== */
body::before {
  content: '';
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 1000;
  opacity: 0.03;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise)'/%3E%3C/svg%3E");
}

/* ========== Vignette Effect ========== */
body::after {
  content: '';
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 999;
  background: radial-gradient(ellipse at center, transparent 40%, rgba(0,0,0,0.4) 100%);
}

/* ========== Page Structure ========== */
.page {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: var(--player-height);
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
  align-items: center;
  padding: var(--space-8) var(--space-6) var(--space-16);
  overflow-y: auto;
  overflow-x: hidden;
  -webkit-overflow-scrolling: touch;
}

.page-content {
  padding-top: var(--space-10);
}

.page-title {
  justify-content: center;
  padding-top: 0;
}

.page::before {
  content: '';
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: 
    radial-gradient(ellipse at 50% 30%, rgba(201,162,39,0.06) 0%, transparent 50%),
    radial-gradient(ellipse at 75% 75%, rgba(74,111,165,0.08) 0%, transparent 45%),
    radial-gradient(ellipse at 25% 80%, rgba(74,111,165,0.06) 0%, transparent 40%),
    linear-gradient(180deg, #1a1a2e 0%, #222240 50%, #1a1a2e 100%);
  z-index: -1;
}

/* Page-specific backgrounds */
.page-title::before {
  background: 
    radial-gradient(ellipse at 50% 25%, rgba(201,162,39,0.12) 0%, transparent 45%),
    radial-gradient(ellipse at 75% 75%, rgba(74,111,165,0.12) 0%, transparent 40%),
    radial-gradient(ellipse at 25% 75%, rgba(74,111,165,0.08) 0%, transparent 40%),
    linear-gradient(180deg, #1a1a2e 0%, #222240 50%, #1a1a2e 100%);
}

.page-content::before {
  background: 
    radial-gradient(ellipse at 50% 30%, rgba(201,162,39,0.06) 0%, transparent 50%),
    radial-gradient(ellipse at 75% 75%, rgba(74,111,165,0.10) 0%, transparent 40%),
    radial-gradient(ellipse at 25% 80%, rgba(74,111,165,0.06) 0%, transparent 40%),
    linear-gradient(180deg, #1a1a2e 0%, #222240 50%, #1a1a2e 100%);
}

/* ========== Content Container ========== */
.content-container {
  max-width: 900px;
  width: 100%;
  margin: 0 auto;
  padding: var(--space-6);
  padding-left: calc(var(--space-6) + 80px);
  position: relative;
  z-index: 1;
}

/* ========== Typography System ========== */
h1, h2, h3, h4 {
  font-family: var(--font-heading);
  color: var(--aged-paper);
  line-height: 1.4;
  margin-bottom: var(--space-4);
}

h1 {
  font-size: 2.2rem;
  letter-spacing: 2px;
  text-shadow: 2px 2px 4px rgba(0,0,0,0.5);
}

h2 {
  font-size: 1.6rem;
  letter-spacing: 1px;
  border-bottom: 2px solid var(--border-subtle);
  padding-bottom: var(--space-3);
  margin-bottom: var(--space-6);
}

h3 {
  font-size: 1.2rem;
  color: var(--muted-gold);
  margin-top: var(--space-6);
  margin-bottom: var(--space-3);
}

h4 {
  font-size: 1rem;
  color: var(--faded-blue);
  font-family: var(--font-body-cn);
  font-weight: 600;
}

p {
  font-size: 1rem;
  line-height: 1.9;
  color: var(--text-primary);
  margin-bottom: var(--space-4);
  text-align: justify;
}

p:last-child {
  margin-bottom: 0;
}

/* ========== Special Text Elements ========== */
.quote {
  border-left: 4px solid var(--muted-gold);
  padding: var(--space-4) var(--space-6);
  margin: var(--space-6) 0;
  background: rgba(201,162,39,0.08);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  font-style: italic;
  color: var(--cream);
  font-size: 1.05rem;
  line-height: 1.8;
}

.quote cite {
  display: block;
  margin-top: var(--space-3);
  font-size: 0.9rem;
  color: var(--muted-gold);
  font-style: normal;
}

.highlight {
  color: var(--muted-gold);
  font-weight: 600;
}

.key-term {
  display: inline-block;
  background: rgba(201,162,39,0.15);
  color: var(--muted-gold);
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-sm);
  font-weight: 600;
  border: 1px solid rgba(201,162,39,0.3);
}

.timestamp {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--faded-blue);
  background: rgba(74,111,165,0.15);
  padding: var(--space-1) var(--space-2);
  border-radius: var(--radius-sm);
  display: inline-block;
  margin-bottom: var(--space-3);
}

/* ========== Cards & Boxes ========== */
.info-card {
  background: rgba(42,42,62,0.8);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  margin: var(--space-6) 0;
  backdrop-filter: blur(8px);
}

.info-card h3 {
  margin-top: 0;
  border-bottom: 1px solid var(--border-subtle);
  padding-bottom: var(--space-3);
}

.data-card {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  background: rgba(26,26,46,0.6);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: var(--space-4) var(--space-6);
  margin: var(--space-2);
  min-width: 120px;
}

.data-card .value {
  font-family: var(--font-heading);
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--muted-gold);
}

.data-card .label {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: var(--space-1);
  text-align: center;
}

.data-row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin: var(--space-4) 0;
  justify-content: center;
}

/* ========== Lists ========== */
ul, ol {
  margin: var(--space-4) 0;
  padding-left: var(--space-6);
}

li {
  margin-bottom: var(--space-3);
  color: var(--text-primary);
  line-height: 1.7;
}

li strong {
  color: var(--aged-paper);
}

/* ========== Tables ========== */
table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-6) 0;
  font-size: 0.95rem;
}

th, td {
  padding: var(--space-3) var(--space-4);
  text-align: left;
  border-bottom: 1px solid var(--border-subtle);
}

th {
  background: rgba(201,162,39,0.1);
  color: var(--muted-gold);
  font-weight: 600;
  font-family: var(--font-ui);
  font-size: 0.9rem;
}

tr:hover {
  background: rgba(201,162,39,0.05);
}

/* ========== Table Responsive Wrapper ========== */
.table-wrapper {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  margin: var(--space-6) 0;
  scrollbar-width: thin;
  scrollbar-color: rgba(201,162,39,0.3) transparent;
}
.table-wrapper table {
  margin: 0;
  min-width: 600px;
}

/* ========== Image Placeholders ========== */
.image-placeholder {
  background: rgba(42,42,62,0.6);
  border: 2px dashed var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: var(--space-8);
  margin: var(--space-6) 0;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.image-placeholder::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: 
    repeating-linear-gradient(
      45deg,
      transparent,
      transparent 20px,
      rgba(201,162,39,0.03) 20px,
      rgba(201,162,39,0.03) 40px
    );
  pointer-events: none;
}

.image-placeholder .icon {
  font-size: 3rem;
  margin-bottom: var(--space-4);
  opacity: 0.6;
}

.image-placeholder .type {
  font-family: var(--font-ui);
  font-size: 0.75rem;
  color: var(--faded-blue);
  background: rgba(74,111,165,0.2);
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-sm);
  display: inline-block;
  margin-bottom: var(--space-3);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.image-placeholder .description {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
  max-width: 500px;
  margin: 0 auto;
}

.image-placeholder .source {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: var(--space-3);
  font-style: italic;
}

/* ========== Image Containers ========== */
.image-container {
  margin: var(--space-6) 0;
  text-align: center;
}

.lecture-image {
  max-width: 100%;
  height: auto;
  max-height: 50vh;
  border-radius: var(--radius-lg);
  border: 2px solid var(--border-subtle);
  box-shadow: 0 4px 20px rgba(0,0,0,0.3);
  object-fit: contain;
}

.image-caption {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: var(--space-3);
  font-style: italic;
  line-height: 1.5;
}

/* ========== Image Layout Variants ========== */

/* Split layout: text + image side by side */
.split-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-8);
  margin: var(--space-6) 0;
  align-items: center;
}
.split-layout .image-container {
  margin: 0;
}
.split-layout .image-container .lecture-image {
  width: 100%;
  object-fit: cover;
  max-height: 45vh;
}

/* Reversed split (image on left) */
.split-layout.split-reverse {
  direction: rtl;
}
.split-layout.split-reverse > * {
  direction: ltr;
}

/* Two images side by side */
.image-grid-2 {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-4);
  margin: var(--space-6) 0;
}
.image-grid-2 .image-container {
  margin: 0;
}

/* Hero/banner image with extended width */
.image-banner {
  margin: var(--space-8) calc(-1 * var(--space-6));
  width: auto;
}
.image-banner .lecture-image {
  max-height: 55vh;
  width: 100%;
  object-fit: cover;
  border-radius: var(--radius-lg);
}

/* Inset image - narrower, centered */
.image-inset {
  max-width: 70%;
  margin: var(--space-6) auto;
}
.image-inset .lecture-image {
  max-height: 35vh;
}

/* Image with visible top border accent */
.image-accent {
  position: relative;
  padding-top: var(--space-3);
}
.image-accent::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 60px;
  height: 3px;
  background: var(--muted-gold);
  border-radius: 2px;
}

/* ========== Page Overflow Indicator ========== */
.page-overflow-indicator {
  position: sticky;
  bottom: 0;
  height: 40px;
  margin-top: -40px;
  background: transparent;
  pointer-events: none;
  z-index: 2;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2px;
  transition: opacity 0.5s ease;
}

.page-overflow-indicator::before,
.page-overflow-indicator::after {
  content: '';
  width: 13px;
  height: 13px;
  border-right: 2px solid var(--muted-gold);
  border-bottom: 2px solid var(--muted-gold);
  animation: indicator-drift 2.4s ease-in-out infinite;
}

.page-overflow-indicator::before {
  opacity: 0.55;
}

.page-overflow-indicator::after {
  opacity: 0.75;
}

.page-overflow-indicator.hidden {
  opacity: 0;
}

@keyframes indicator-drift {
  0%, 100% {
    transform: rotate(45deg) translateY(0);
  }
  50% {
    transform: rotate(45deg) translateY(4px);
  }
}

/* ========== Navigation Arrows ========== */
.nav-arrow {
  position: fixed;
  top: 50%;
  transform: translateY(-50%);
  width: 48px;
  height: 48px;
  background: rgba(42,42,62,0.8);
  border: 1px solid var(--border-subtle);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  z-index: 100;
  transition: all var(--transition-normal);
  backdrop-filter: blur(8px);
}

.nav-arrow:hover {
  background: rgba(201,162,39,0.2);
  border-color: var(--muted-gold);
  transform: translateY(-50%) scale(1.1);
}

.nav-arrow svg {
  width: 24px;
  height: 24px;
  fill: var(--aged-paper);
}

.nav-arrow.prev {
  left: var(--space-4);
}

.nav-arrow.next {
  right: var(--space-4);
}

/* ========== Home Button ========== */
.home-btn {
  position: fixed;
  top: var(--space-4);
  left: var(--space-4);
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px;
  background: rgba(42,42,62,0.8);
  border: 1px solid var(--border-subtle);
  border-radius: 24px;
  color: var(--aged-paper);
  text-decoration: none;
  font-family: 'Noto Sans SC', sans-serif;
  font-size: 14px;
  font-weight: 500;
  z-index: 100;
  transition: all var(--transition-normal);
  backdrop-filter: blur(8px);
}

.home-btn:hover {
  background: rgba(201,162,39,0.2);
  border-color: var(--muted-gold);
  transform: scale(1.05);
}

.home-btn svg {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
}

.home-btn-text {
  white-space: nowrap;
}

@media (max-width: 768px) {
  .home-btn {
    padding: 10px;
    border-radius: 50%;
  }
  .home-btn-text {
    display: none;
  }
}

/* ========== Page Indicator ========== */
.page-indicator {
  position: fixed;
  right: var(--space-4);
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  z-index: 100;
}

.page-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: rgba(201,162,39,0.3);
  border: 1px solid rgba(201,162,39,0.5);
  cursor: pointer;
  transition: all var(--transition-normal);
}

.page-dot.active {
  background: var(--muted-gold);
  transform: scale(1.3);
  box-shadow: 0 0 10px rgba(201,162,39,0.5);
}

.page-dot:hover {
  background: rgba(201,162,39,0.6);
}

/* ========== Audio Player ========== */
.audio-player {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: 64px;
  background: rgba(26,26,46,0.95);
  backdrop-filter: blur(12px);
  border-top: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  padding: 0 var(--space-6);
  gap: var(--space-4);
  z-index: 1000;
}

.audio-player .play-btn {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 2px solid var(--muted-gold);
  background: transparent;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
  flex-shrink: 0;
}

.audio-player .play-btn:hover {
  background: var(--muted-gold);
}

.audio-player .play-btn svg {
  width: 18px;
  height: 18px;
  fill: var(--muted-gold);
  transition: fill var(--transition-fast);
}

.audio-player .play-btn:hover svg {
  fill: var(--bg-deep);
}

.progress-container {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}

.progress-bar {
  width: 100%;
  height: 4px;
  background: rgba(201,162,39,0.2);
  border-radius: 2px;
  cursor: pointer;
  position: relative;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--faded-blue), var(--muted-gold));
  border-radius: 2px;
  width: 0%;
  transition: width 0.1s linear;
  position: relative;
}

.progress-fill::after {
  content: '';
  position: absolute;
  right: -6px;
  top: 50%;
  transform: translateY(-50%);
  width: 12px;
  height: 12px;
  background: var(--muted-gold);
  border-radius: 50%;
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.progress-bar:hover .progress-fill::after {
  opacity: 1;
}

.progress-markers {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 100%;
  pointer-events: none;
}

.progress-marker {
  position: absolute;
  top: -2px;
  width: 2px;
  height: 8px;
  background: rgba(201,162,39,0.4);
  border-radius: 1px;
}

.time-display {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-muted);
  display: flex;
  justify-content: space-between;
}

.volume-control {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.volume-slider {
  width: 80px;
  height: 4px;
  -webkit-appearance: none;
  background: rgba(201,162,39,0.2);
  border-radius: 2px;
  outline: none;
}

.volume-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 12px;
  height: 12px;
  background: var(--muted-gold);
  border-radius: 50%;
  cursor: pointer;
}

/* ========== Page Transition Animation ========== */
.page {
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease, visibility 0.6s ease;
}

.page.active {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
  z-index: 1;
}

/* ========== Title Page Specific ========== */
.title-page {
  text-align: center;
  padding-left: var(--space-6);
}

.title-page h1 {
  font-size: 2.5rem;
  margin-bottom: var(--space-4);
  background: linear-gradient(135deg, var(--aged-paper), var(--muted-gold));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
  background-clip: text;
}

.title-subtitle {
  font-family: var(--font-body-cn);
  font-size: 1.2rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-8);
}

.title-meta {
  font-family: var(--font-ui);
  font-size: 0.9rem;
  color: var(--faded-blue);
  margin-bottom: var(--space-8);
}

.objectives {
  text-align: left;
  max-width: 700px;
  margin: 0 auto;
}

.objectives h3 {
  text-align: center;
  margin-bottom: var(--space-6);
}

.objectives ul {
  list-style: none;
  padding: 0;
}

.objectives li {
  padding: var(--space-3) var(--space-4);
  border-left: 3px solid var(--faded-blue);
  margin-bottom: var(--space-3);
  background: rgba(74,111,165,0.08);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  transition: all var(--transition-normal);
}

.objectives li:hover {
  background: rgba(74,111,165,0.15);
  border-left-color: var(--muted-gold);
}

@media (min-width: 1200px) {
  .content-container {
    max-width: 1000px;
  }
  .lecture-image {
    max-height: 75vh;
  }
}

/* ========== Responsive Design ========== */
@media (max-width: 1024px) {
  :root {
    --player-height: 56px;
  }
  .nav-arrow {
    width: 40px;
    height: 40px;
  }
  .nav-arrow svg {
    width: 20px;
    height: 20px;
  }
  .page-indicator {
    right: var(--space-3);
  }
  .page-dot {
    width: 8px;
    height: 8px;
  }
  .lecture-image {
    max-height: 40vh;
  }
  .content-container {
    max-width: 90vw;
  }
  h1 { font-size: 2rem; }
  h2 { font-size: 1.4rem; }
}

@media (max-width: 768px) {
  :root {
    --player-height: 48px;
  }
  .page {
    padding: var(--space-6) var(--space-4) var(--space-12);
  }
  .page-content {
    padding-top: var(--space-8);
  }
  .page-title {
    padding-top: 0;
  }
  h1 { font-size: 1.6rem; }
  h2 { font-size: 1.2rem; }
  h3 { font-size: 1.05rem; }
  .content-container {
    max-width: 100%;
    padding: var(--space-3);
  }
  .nav-arrow {
    width: 36px;
    height: 36px;
    top: auto;
    bottom: calc(var(--player-height) + var(--space-4));
    transform: none;
  }
  .nav-arrow:hover {
    transform: scale(1.1);
  }
  .nav-arrow.prev { left: var(--space-2); }
  .nav-arrow.next { right: var(--space-2); }
  .page-indicator {
    top: auto;
    bottom: calc(var(--player-height) + var(--space-2));
    right: 50%;
    transform: translateX(50%);
    flex-direction: row;
    gap: var(--space-2);
  }
  .audio-player {
    height: var(--player-height);
    padding: 0 var(--space-3);
  }
  .volume-control {
    display: none;
  }
  .data-card {
    min-width: 80px;
    padding: var(--space-2) var(--space-3);
  }
  .data-card .value {
    font-size: 1rem;
  }
  .data-card .label {
    font-size: 0.7rem;
  }
  .image-placeholder {
    padding: var(--space-6) var(--space-4);
  }
  .image-placeholder .icon {
    font-size: 2rem;
  }
  .lecture-image {
    max-height: 30vh;
  }
  .info-card {
    padding: var(--space-4);
  }
  .quote {
    padding: var(--space-3) var(--space-4);
    font-size: 0.95rem;
  }
  table {
    font-size: 0.85rem;
  }
  th, td {
    padding: var(--space-2) var(--space-3);
  }
  .page-overflow-indicator {
    height: 32px;
    margin-top: -32px;
    gap: 1px;
  }
  .page-overflow-indicator::before,
  .page-overflow-indicator::after {
    width: 9px;
    height: 9px;
    border-width: 1.5px;
  }
  
  /* Mobile: collapse split-layout to single column */
  .split-layout {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }
  .split-layout.split-reverse {
    direction: ltr;
  }
  .split-layout .image-container .lecture-image {
    max-height: 30vh;
  }
  
  /* Mobile: reduce banner margins */
  .image-banner {
    margin: var(--space-4) calc(-1 * var(--space-3));
  }
  .image-banner .lecture-image {
    max-height: 35vh;
  }
  
  /* Mobile: collapse image grid to single column */
  .image-grid-2 {
    grid-template-columns: 1fr;
    gap: var(--space-3);
  }
  
  /* Mobile: full width for inset images */
  .image-inset {
    max-width: 100%;
  }
  .image-inset .lecture-image {
    max-height: 25vh;
  }
}

@media (max-width: 375px) {
  h1 { font-size: 1.4rem; }
  h2 { font-size: 1.1rem; }
  .lecture-image {
    max-height: 25vh;
  }
  .nav-arrow {
    width: 30px;
    height: 30px;
  }
  .data-row {
    gap: var(--space-2);
  }
  .data-card {
    min-width: 70px;
    padding: var(--space-2);
  }
}

/* ========== Keyboard Focus Styles ========== */
.nav-arrow:focus,
.page-dot:focus,
.play-btn:focus {
  outline: 2px solid var(--muted-gold);
  outline-offset: 2px;
}

/* ========== Scrollbar Styling ========== */
::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-deep);
}

::-webkit-scrollbar-thumb {
  background: rgba(201,162,39,0.3);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(201,162,39,0.5);
}