:root {
  --bg-primary: #0b0f17;
  --bg-surface: #111827;
  --bg-subtle: #1a2234;
  --border-color: #232d3f;
  --border-focus: #38bdf8;
  --text-primary: #f8fafc;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --accent: #38bdf8;
  --accent-hover: #0ea5e9;
  --accent-subtle: rgba(56, 189, 248, 0.12);
  --accent-contrast: #0b0f17;
  --danger: #ef4444;
  --danger-subtle: rgba(239, 68, 68, 0.12);
  --success: #10b981;
  --warning: #f59e0b;

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;

  --text-xs: 0.75rem;
  --text-sm: 0.844rem;
  --text-base: 0.95rem;
  --text-lg: 1.125rem;
  --text-xl: 1.35rem;
  --text-2xl: 1.625rem;

  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;

  --nav-height: 56px;
  --header-height: 54px;
  --sidebar-width: 220px;
  --master-width: 330px;
  --touch-target: 48px;
}

[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-subtle: #f1f5f9;
  --border-color: #e2e8f0;
  --border-focus: #0284c7;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --accent: #0284c7;
  --accent-hover: #0369a1;
  --accent-subtle: rgba(2, 132, 199, 0.08);
  --accent-contrast: #ffffff;
  --danger: #dc2626;
  --danger-subtle: rgba(220, 38, 38, 0.08);
  --success: #059669;
  --warning: #d97706;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html, body {
  width: 100%;
  height: 100dvh;
  height: 100vh;
  overflow: hidden;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -webkit-tap-highlight-color: transparent;
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* Master Layout Framework */
#app-root {
  display: flex;
  flex-direction: column;
  width: 100%;
  height: 100dvh;
  height: 100vh;
  min-height: 0;
  overflow: hidden;
}

/* App Header */
.app-header {
  flex-shrink: 0;
  height: var(--header-height);
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  padding: 0 var(--space-4);
  padding-top: env(safe-area-inset-top, 0px);
  display: flex;
  align-items: center;
  justify-content: space-between;
  z-index: 40;
}

.brand-title {
  font-size: var(--text-base);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: var(--space-2);
  text-decoration: none;
}

.brand-title .brand-mark {
  display: inline-block;
  width: 8px;
  height: 8px;
  background-color: var(--accent);
}

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

/* Base Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-height: var(--touch-target);
  min-width: var(--touch-target);
  padding: 0 var(--space-4);
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  font-family: inherit;
  font-size: var(--text-sm);
  font-weight: 500;
  cursor: pointer;
  text-decoration: none;
  transition: background-color 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}

.btn:hover {
  background-color: var(--bg-subtle);
  border-color: var(--border-focus);
}

.btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.btn-icon {
  width: var(--touch-target);
  height: var(--touch-target);
  padding: 0;
}

.btn-primary {
  background-color: var(--accent);
  border-color: var(--accent);
  color: var(--accent-contrast);
  font-weight: 600;
}

.btn-primary:hover {
  background-color: var(--accent-hover);
  border-color: var(--accent-hover);
}

.btn-danger {
  color: var(--danger);
  border-color: var(--border-color);
}

.btn-danger:hover {
  background-color: var(--danger-subtle);
  border-color: var(--danger);
}

.btn-sm {
  min-height: 36px;
  padding: 0 var(--space-3);
  font-size: var(--text-xs);
}

/* Banners */
.offline-banner {
  display: none;
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--warning);
  color: var(--warning);
  font-size: var(--text-xs);
  font-weight: 600;
  padding: var(--space-2) var(--space-4);
  text-align: center;
  flex-shrink: 0;
}

.offline-banner.visible {
  display: block;
}

.install-banner {
  display: none;
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  padding: var(--space-2) var(--space-4);
  flex-shrink: 0;
}

.install-banner.visible {
  display: block;
}

.install-banner-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
  width: 100%;
}

.install-banner-text {
  font-size: var(--text-sm);
  color: var(--text-secondary);
}

/* App Body (Houses desktop sidebar + workspace) */
.app-body {
  display: flex;
  flex: 1;
  min-height: 0;
  width: 100%;
  overflow: hidden;
}

/* Desktop Sidebar Nav */
.desktop-sidebar {
  display: none;
  width: var(--sidebar-width);
  background-color: var(--bg-primary);
  border-right: 1px solid var(--border-color);
  flex-direction: column;
  flex-shrink: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
}

.sidebar-nav-list {
  list-style: none;
  padding: var(--space-3) 0;
}

.sidebar-nav-item a {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: 0 var(--space-4);
  height: var(--touch-target);
  color: var(--text-secondary);
  text-decoration: none;
  font-size: var(--text-sm);
  font-weight: 600;
  border-left: 3px solid transparent;
  transition: all 0.15s ease;
}

.sidebar-nav-item a:hover {
  background-color: var(--bg-subtle);
  color: var(--text-primary);
}

.sidebar-nav-item a.active {
  color: var(--accent);
  background-color: var(--accent-subtle);
  border-left-color: var(--accent);
}

.sidebar-nav-item svg {
  width: 18px;
  height: 18px;
  stroke: currentColor;
  stroke-width: 2;
  fill: none;
}

/* Main Workspace */
.main-workspace {
  flex: 1;
  min-height: 0;
  width: 100%;
  display: flex;
  overflow: hidden;
}

/* Phone View Container (Single scrollable container) */
.phone-pane {
  flex: 1;
  min-height: 0;
  width: 100%;
  overflow-y: auto;
  overscroll-behavior: contain;
  padding: var(--space-4);
}

/* Tablet & Desktop Split View (Two Panes) */
.split-master-pane {
  display: none;
  width: var(--master-width);
  border-right: 1px solid var(--border-color);
  min-height: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  padding: var(--space-4);
  flex-shrink: 0;
}

.split-detail-pane {
  display: none;
  flex: 1;
  min-height: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  padding: var(--space-5) var(--space-6);
}

/* Tablet Mode (768px - 1199px) */
@media (min-width: 768px) {
  .phone-pane.has-split {
    display: none;
  }
  .split-master-pane {
    display: block;
  }
  .split-detail-pane {
    display: block;
  }
}

/* Desktop Mode (1200px+) */
@media (min-width: 1200px) {
  .desktop-sidebar {
    display: flex;
  }
  .bottom-nav {
    display: none !important;
  }
  .app-header .brand-title {
    display: none;
  }
  .desktop-sidebar .brand-title {
    display: flex;
    padding: var(--space-4);
    height: var(--header-height);
    border-bottom: 1px solid var(--border-color);
  }
}

/* Bottom Navigation (Phone & Tablet) */
.bottom-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  z-index: 40;
  height: calc(var(--nav-height) + env(safe-area-inset-bottom, 0px));
  padding-bottom: env(safe-area-inset-bottom, 0px);
  background-color: var(--bg-primary);
  border-top: 1px solid var(--border-color);
  flex-shrink: 0;
}

.bottom-nav-inner {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  width: 100%;
  height: var(--nav-height);
}

.nav-tab {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: var(--text-xs);
  font-weight: 600;
  min-height: var(--touch-target);
  transition: color 0.15s ease;
}

.nav-tab svg {
  width: 20px;
  height: 20px;
  stroke: currentColor;
  stroke-width: 2;
  fill: none;
}

.nav-tab.active {
  color: var(--accent);
}

/* Phone bottom padding compensation */
@media (max-width: 1199px) {
  .phone-pane, .split-master-pane, .split-detail-pane {
    padding-bottom: calc(var(--nav-height) + var(--space-6) + env(safe-area-inset-bottom, 0px));
  }
}

/* Page Headers */
.page-header {
  padding-bottom: var(--space-3);
  border-bottom: 1px solid var(--border-color);
  margin-bottom: var(--space-4);
}

.page-title {
  font-size: var(--text-xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  margin-bottom: var(--space-1);
}

.page-subtitle {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.4;
}

/* Fluid Row List */
.row-list {
  list-style: none;
  border-top: 1px solid var(--border-color);
}

/* Uniform Topic Row - Same structure and height */
.topic-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-3) var(--space-2);
  border-bottom: 1px solid var(--border-color);
  text-decoration: none;
  color: inherit;
  min-height: 74px;
  transition: background-color 0.15s ease;
}

.topic-row:hover, .topic-row:focus-visible, .topic-row.active-topic {
  background-color: var(--accent-subtle);
  outline: none;
}

.topic-row-left {
  display: flex;
  align-items: flex-start;
  gap: var(--space-3);
  flex: 1;
  min-width: 0;
}

.topic-row-num {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--text-muted);
  width: 24px;
  flex-shrink: 0;
  margin-top: 2px;
}

.topic-row-body {
  flex: 1;
  min-width: 0;
  padding-right: var(--space-2);
}

.topic-row-title {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--text-primary);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  margin-bottom: 2px;
}

.topic-row-summary {
  font-size: var(--text-xs);
  color: var(--text-secondary);
  line-height: 1.35;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.topic-row-right {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex-shrink: 0;
}

.topic-row-progress {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--text-muted);
}

.topic-row-progress.done {
  color: var(--accent);
  font-weight: 600;
}

/* Topic Section Switcher (Tabs on Mobile, Sticky Rail on Desktop) */
.section-switcher {
  display: flex;
  gap: var(--space-1);
  overflow-x: auto;
  border-bottom: 1px solid var(--border-color);
  margin-bottom: var(--space-5);
  padding-bottom: var(--space-1);
  scrollbar-width: none;
  -webkit-overflow-scrolling: touch;
}

.section-switcher::-webkit-scrollbar {
  display: none;
}

.section-tab-btn {
  background: transparent;
  border: none;
  border-bottom: 2px solid transparent;
  color: var(--text-secondary);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: var(--space-2) var(--space-3);
  cursor: pointer;
  white-space: nowrap;
  min-height: var(--touch-target);
  display: inline-flex;
  align-items: center;
}

.section-tab-btn:hover {
  color: var(--text-primary);
}

.section-tab-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

/* Reading Typography: 75ch constraint for optimal line length */
.reading-content {
  max-width: 75ch;
}

.reading-content p {
  font-size: var(--text-base);
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: var(--space-4);
}

.reading-content p:last-child {
  margin-bottom: 0;
}

/* Multi-Column CSS Grids for Desktop */
.content-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
  width: 100%;
}

@media (min-width: 900px) {
  .content-grid-2col {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1400px) {
  .content-grid-3col {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* Expandable / Collapsible Plain Rows */
.accordion-list {
  list-style: none;
  border-top: 1px solid var(--border-color);
}

.accordion-item {
  border-bottom: 1px solid var(--border-color);
}

.accordion-header {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-3) 0;
  background: transparent;
  border: none;
  color: var(--text-primary);
  font-family: inherit;
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  text-align: left;
  min-height: var(--touch-target);
  gap: var(--space-3);
}

.accordion-header:hover {
  color: var(--accent);
}

.accordion-icon {
  width: 16px;
  height: 16px;
  stroke: currentColor;
  stroke-width: 2;
  fill: none;
  transition: transform 0.2s ease;
  flex-shrink: 0;
}

.accordion-item.open .accordion-icon {
  transform: rotate(180deg);
}

.accordion-body {
  display: none;
  padding-bottom: var(--space-4);
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.6;
}

.accordion-item.open .accordion-body {
  display: block;
}

/* Mono Diagrams (Plain Characters Only) */
.text-diagram {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  padding: var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--accent);
  line-height: 1.35;
  overflow-x: auto;
  white-space: pre;
  margin: var(--space-3) 0;
}

/* Metadata & Checkboxes */
.checklist-item {
  display: flex;
  align-items: flex-start;
  gap: var(--space-3);
  padding: var(--space-3) 0;
  border-bottom: 1px solid var(--border-color);
  min-height: var(--touch-target);
}

.checklist-checkbox {
  appearance: none;
  -webkit-appearance: none;
  width: 22px;
  height: 22px;
  border: 2px solid var(--border-color);
  background: var(--bg-surface);
  cursor: pointer;
  margin-top: 2px;
  flex-shrink: 0;
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.checklist-checkbox:checked {
  background-color: var(--accent);
  border-color: var(--accent);
}

.checklist-checkbox:checked::after {
  content: "";
  width: 6px;
  height: 11px;
  border: solid var(--accent-contrast);
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
  margin-bottom: 2px;
}

/* Utility Badges */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 2px 6px;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
}

.badge-accent {
  background-color: var(--accent-subtle);
  border-color: var(--accent);
  color: var(--accent);
}

/* Search input */
.input-field {
  width: 100%;
  min-height: var(--touch-target);
  padding: 0 var(--space-3);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  font-family: inherit;
  font-size: var(--text-sm);
}

.input-field:focus {
  outline: none;
  border-color: var(--border-focus);
}

/* Star Favorite Button */
.star-btn {
  background: transparent;
  border: none;
  color: var(--text-muted);
  width: var(--touch-target);
  height: var(--touch-target);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  padding: 0;
}

.star-btn svg {
  width: 20px;
  height: 20px;
  stroke: currentColor;
  fill: transparent;
  stroke-width: 2;
}

.star-btn.active {
  color: var(--warning);
}

.star-btn.active svg {
  fill: currentColor;
}

/* Notes Textarea */
.notes-textarea {
  width: 100%;
  min-height: 140px;
  padding: var(--space-3);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  font-family: inherit;
  font-size: var(--text-sm);
  line-height: 1.5;
  resize: vertical;
}

.notes-textarea:focus {
  outline: none;
  border-color: var(--border-focus);
}

/* News Image */
.news-media-wrap {
  width: 100%;
  aspect-ratio: 16 / 9;
  background-color: var(--bg-subtle);
  overflow: hidden;
  margin-bottom: var(--space-3);
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border-color);
}

.news-image {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}

.news-image-fallback {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  color: var(--text-muted);
  font-size: var(--text-xs);
  font-family: var(--font-mono);
}

/* Loading Spinner */
.loading-indicator {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-8) 0;
  color: var(--text-muted);
  font-size: var(--text-sm);
  font-family: var(--font-mono);
}

.spinner {
  width: 18px;
  height: 18px;
  border: 2px solid var(--border-color);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* Filter tabs for Favorites */
.tab-filter-bar {
  display: flex;
  border-bottom: 1px solid var(--border-color);
  margin-bottom: var(--space-4);
  gap: var(--space-2);
  overflow-x: auto;
}

.tab-filter-btn {
  background: transparent;
  border: none;
  border-bottom: 2px solid transparent;
  color: var(--text-secondary);
  font-size: var(--text-sm);
  font-weight: 600;
  padding: var(--space-3) var(--space-2);
  cursor: pointer;
  min-height: var(--touch-target);
  white-space: nowrap;
}

.tab-filter-btn.active {
  color: var(--text-primary);
  border-bottom-color: var(--accent);
}

/* Modals */
.modal-overlay {
  position: fixed;
  inset: 0;
  z-index: 50;
  background-color: rgba(0, 0, 0, 0.75);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-4);
}

.modal-content {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  width: 100%;
  max-width: 520px;
  max-height: 90vh;
  overflow-y: auto;
  padding: var(--space-5);
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-4);
  border-bottom: 1px solid var(--border-color);
  padding-bottom: var(--space-3);
}

.modal-title {
  font-size: var(--text-lg);
  font-weight: 700;
}

.form-group {
  margin-bottom: var(--space-4);
}

.form-label {
  display: block;
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: var(--space-1);
}

.form-actions {
  display: flex;
  justify-content: flex-end;
  gap: var(--space-2);
  margin-top: var(--space-5);
}

.status-message {
  padding: var(--space-4);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  margin-bottom: var(--space-4);
  font-size: var(--text-sm);
}

.status-message.error {
  border-color: var(--danger);
  color: var(--danger);
}

.empty-state {
  padding: var(--space-8) var(--space-4);
  text-align: center;
  color: var(--text-muted);
}

.empty-state-title {
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: var(--space-1);
}

.empty-state-desc {
  font-size: var(--text-sm);
  max-width: 320px;
  margin: 0 auto;
}

/* ==========================================================
   Full-Text Search & Topic Sub-Navigation (Phase 4 & 5)
   ========================================================== */
mark {
  background-color: var(--accent-subtle);
  color: var(--accent);
  padding: 1px 3px;
  border-radius: 2px;
  font-weight: 600;
}

.search-results-container {
  padding: var(--space-2) 0;
}

.search-results-summary {
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  color: var(--text-muted);
  margin-bottom: var(--space-3);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.search-group {
  margin-bottom: var(--space-4);
  border-bottom: 1px solid var(--border-color);
  padding-bottom: var(--space-3);
}

.search-group:last-child {
  border-bottom: none;
}

.search-group-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-2) 0;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 600;
}

.search-result-item {
  display: block;
  padding: var(--space-3);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  margin-bottom: var(--space-2);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.15s ease, background-color 0.15s ease;
}

.search-result-item:hover, .search-result-item:focus-visible {
  border-color: var(--border-focus);
  background-color: var(--bg-subtle);
  outline: none;
}

.search-result-top {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-1);
}

.search-cat-badge {
  font-size: 10px;
  font-family: var(--font-mono);
  text-transform: uppercase;
  padding: 1px 6px;
  border: 1px solid var(--border-color);
  background-color: var(--bg-primary);
  color: var(--text-secondary);
  flex-shrink: 0;
}

.search-result-title {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--text-primary);
}

.search-result-snippet {
  font-size: var(--text-xs);
  color: var(--text-secondary);
  line-height: 1.45;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Detail Section Headers & Sticky Sub-Navigation */
.topic-detail-section {
  padding: var(--space-5) 0;
  border-bottom: 1px solid var(--border-color);
}

.topic-detail-section:last-of-type {
  border-bottom: none;
}

.sticky-subnav {
  position: sticky;
  top: 0;
  z-index: 25;
  background-color: var(--bg-primary);
  padding: var(--space-2) 0;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  gap: var(--space-1);
  overflow-x: auto;
  scrollbar-width: none;
}

.sticky-subnav::-webkit-scrollbar {
  display: none;
}

.subnav-tab-btn {
  background: transparent;
  border: none;
  border-bottom: 2px solid transparent;
  color: var(--text-secondary);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: var(--space-2) var(--space-3);
  cursor: pointer;
  white-space: nowrap;
  min-height: 40px;
  display: inline-flex;
  align-items: center;
}

.subnav-tab-btn:hover {
  color: var(--text-primary);
}

.subnav-tab-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.learning-level-block {
  margin-bottom: var(--space-4);
  padding: var(--space-4);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
}

.learning-level-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-2);
}

.learning-level-title {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--text-primary);
}

.learning-level-outcome {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  margin-bottom: var(--space-3);
  line-height: 1.5;
}

.learning-steps-list {
  list-style: decimal inside;
  color: var(--text-secondary);
  font-size: var(--text-sm);
  line-height: 1.6;
}

.learning-steps-list li {
  margin-bottom: var(--space-2);
  padding-left: var(--space-1);
}

.failure-mode-item {
  padding: var(--space-4);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  margin-bottom: var(--space-3);
}

.failure-symptom {
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--danger);
  margin-bottom: var(--space-2);
  display: flex;
  align-items: flex-start;
  gap: var(--space-2);
}

.failure-rootcause {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  margin-bottom: var(--space-2);
  line-height: 1.5;
}

.failure-fix {
  font-size: var(--text-sm);
  color: var(--text-primary);
  background-color: var(--bg-subtle);
  border-left: 3px solid var(--accent);
  padding: var(--space-2) var(--space-3);
  line-height: 1.5;
}

.resource-link-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-3) var(--space-4);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  text-decoration: none;
  color: inherit;
  transition: border-color 0.15s ease, background-color 0.15s ease;
  min-height: var(--touch-target);
}

.resource-link-item:hover, .resource-link-item:focus-visible {
  border-color: var(--border-focus);
  background-color: var(--bg-subtle);
}

.glossary-card {
  padding: var(--space-3) var(--space-4);
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
}

.glossary-term {
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-1);
  font-family: var(--font-mono);
}

.glossary-def {
  font-size: var(--text-xs);
  color: var(--text-secondary);
  line-height: 1.5;
}

.progress-track {
  width: 100%;
  height: 6px;
  background-color: var(--bg-subtle);
  border: 1px solid var(--border-color);
  margin-top: var(--space-2);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background-color: var(--accent);
  transition: width 0.3s ease;
}