/* ============================================================
   Components — Buttons, Tags, Cards, Sidebar Items, Inputs
   ============================================================ */

/* === Icon Button === */
.icon-btn {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  background: transparent;
  border: 1px solid transparent;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  position: relative;
}
.icon-btn:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}
.icon-btn.active {
  background: var(--brand-light);
  color: var(--brand-primary);
}
.icon-btn svg {
  width: 18px;
  height: 18px;
  stroke-width: 1.8;
}

/* === Tooltip === */
.icon-btn[title]::after {
  content: attr(title);
  position: absolute;
  top: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%) translateY(-4px);
  background: var(--text-primary);
  color: var(--text-inverse);
  font-size: 0.75rem;
  padding: 5px 10px;
  border-radius: var(--radius-sm);
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: all var(--transition-fast);
  z-index: 200;
}
.icon-btn[title]::before {
  content: '';
  position: absolute;
  top: calc(100% + 3px);
  left: 50%;
  transform: translateX(-50%) translateY(-4px);
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-bottom: 5px solid var(--text-primary);
  opacity: 0;
  pointer-events: none;
  transition: all var(--transition-fast);
  z-index: 200;
}
.icon-btn[title]:hover::after {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}
.icon-btn[title]:hover::before {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* === Search Box === */
.search-box {
  position: relative;
  margin: 0 12px 12px;
}
.search-box input {
  width: 100%;
  padding: 8px 12px 8px 36px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-default);
  background: var(--bg-input);
  color: var(--text-primary);
  font-size: 0.875rem;
  font-family: var(--font-sans);
  outline: none;
  transition: all var(--transition-fast);
}
.search-box input::placeholder {
  color: var(--text-tertiary);
}
.search-box input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--brand-light);
}
.search-box svg {
  position: absolute;
  left: 11px;
  top: 50%;
  transform: translateY(-50%);
  width: 16px;
  height: 16px;
  color: var(--text-tertiary);
  stroke-width: 1.8;
}

/* === Sidebar Section === */
.sidebar-section {
  margin-bottom: 4px;
}
.sidebar-section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 16px;
  font-size: 0.6875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-tertiary);
  cursor: pointer;
  user-select: none;
  transition: color var(--transition-fast);
  border-radius: var(--radius-sm);
  margin: 0 8px;
}
.sidebar-section-header:hover {
  color: var(--text-secondary);
  background: var(--bg-hover);
}
.sidebar-section-header svg {
  width: 14px;
  height: 14px;
  transition: transform var(--transition-fast);
  stroke-width: 2;
}
.sidebar-section.collapsed .sidebar-section-header svg {
  transform: rotate(-90deg);
}
.sidebar-section.collapsed .sidebar-section-items {
  display: none;
}

/* === Sidebar Link === */
.sidebar-link {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 16px;
  margin: 0 8px;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 450;
  transition: all var(--transition-fast);
  position: relative;
}
.sidebar-link:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}
.sidebar-link.active {
  background: var(--brand-light);
  color: var(--brand-primary);
  font-weight: 600;
}
.sidebar-link.active::before {
  content: '';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  width: 3px;
  height: 16px;
  background: var(--brand-primary);
  border-radius: 0 2px 2px 0;
}
.sidebar-link-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--border-default);
  flex-shrink: 0;
}
.sidebar-link.active .sidebar-link-dot {
  background: var(--brand-primary);
}

/* === Theme Picker Dropdown === */
.theme-picker {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  padding: 12px;
  min-width: 220px;
  z-index: 200;
  opacity: 0;
  transform: translateY(8px) scale(0.96);
  pointer-events: none;
  transition: all var(--transition-fast);
}
.theme-picker.show {
  opacity: 1;
  transform: translateY(0) scale(1);
  pointer-events: auto;
}
.theme-picker-title {
  font-size: 0.6875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-tertiary);
  margin-bottom: 10px;
  padding: 0 4px;
}
.theme-colors {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  margin-bottom: 12px;
}
.theme-color-btn {
  width: 100%;
  aspect-ratio: 1;
  border-radius: var(--radius-md);
  border: 2px solid transparent;
  cursor: pointer;
  transition: all var(--transition-fast);
  position: relative;
}
.theme-color-btn:hover {
  transform: scale(1.08);
}
.theme-color-btn.active {
  border-color: var(--text-primary);
}
.theme-color-btn.active::after {
  content: '';
  position: absolute;
  inset: 3px;
  border-radius: calc(var(--radius-md) - 3px);
  border: 2px solid white;
}

.theme-divider {
  height: 1px;
  background: var(--border-divider);
  margin: 10px 0;
}

/* === Accent Color Swatches === */
.accent-blue   { background: #1E6BA8; }
.accent-purple { background: #6B2D8F; }
.accent-green  { background: #2E8B57; }
.accent-red    { background: #C41E3A; }
.accent-brown  { background: #8B5A2B; }
.accent-yellow { background: #D4A017; }
.accent-navy   { background: #10206B; }
.accent-mint   { background: #5E8B7E; }

/* === Hero Card (homepage) === */
.hero {
  padding: 64px 40px 48px;
  text-align: center;
  max-width: 720px;
  margin: 0 auto;
}
.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 14px;
  border-radius: 100px;
  background: var(--brand-light);
  color: var(--brand-primary);
  font-size: 0.8125rem;
  font-weight: 600;
  margin-bottom: 20px;
  border: 1px solid rgba(0,0,0,0.04);
}
.hero-title {
  font-size: 2.25rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  margin-bottom: 12px;
  line-height: 1.2;
}
.hero-subtitle {
  font-size: 1.0625rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 32px;
}
.hero-meta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  font-size: 0.875rem;
  color: var(--text-tertiary);
}
.hero-meta span {
  display: flex;
  align-items: center;
  gap: 5px;
}

/* === Platform Cards === */
.platform-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px;
  max-width: 720px;
  margin: 0 auto 48px;
  padding: 0 24px;
}
.platform-card {
  display: flex;
  flex-direction: column;
  padding: 28px;
  border-radius: var(--radius-xl);
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-base);
  cursor: pointer;
  text-align: left;
  position: relative;
  overflow: hidden;
}
.platform-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--brand-primary), var(--brand-hover));
  opacity: 0.7;
  transition: opacity var(--transition-base), height var(--transition-base);
}
.platform-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}
.platform-card:hover::before {
  opacity: 1;
  height: 4px;
}
.platform-card-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 16px;
  font-size: 20px;
  font-weight: 700;
  color: white;
}
.platform-card-icon.pta {
  background: linear-gradient(135deg, #1E6BA8, #2E8B57);
}
.platform-card-icon.educoder {
  background: linear-gradient(135deg, #6B2D8F, #1E6BA8);
}
.platform-card-title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 6px;
  color: var(--text-primary);
}
.platform-card-desc {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 16px;
}
.platform-card-count {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  font-weight: 500;
  margin-top: auto;
}

/* === Chapter Cards === */
.chapter-section {
  max-width: 720px;
  margin: 0 auto 48px;
  padding: 0 24px;
}
.chapter-section-title {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.chapter-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
}
.chapter-card {
  display: block;
  padding: 20px;
  border-radius: var(--radius-lg);
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  box-shadow: var(--shadow-sm);
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}
.chapter-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
  border-color: var(--brand-primary);
}
.chapter-card:hover .chapter-card-tag {
  background: var(--brand-primary);
  color: var(--text-inverse);
}
.chapter-card-tag {
  display: inline-block;
  padding: 2px 8px;
  border-radius: 100px;
  font-size: 0.6875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 10px;
  background: var(--brand-light);
  color: var(--brand-primary);
}
.chapter-card-title {
  font-size: 0.9375rem;
  font-weight: 600;
  margin-bottom: 6px;
  color: var(--text-primary);
}
.chapter-card-desc {
  font-size: 0.8125rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* === Footer === */
.site-footer {
  text-align: center;
  padding: 32px 24px;
  color: var(--text-tertiary);
  font-size: 0.8125rem;
  border-top: 1px solid var(--border-divider);
  margin-top: auto;
}

/* === Responsive === */
@media (max-width: 767px) {
  .platform-grid {
    grid-template-columns: 1fr;
  }
  .chapter-grid {
    grid-template-columns: 1fr;
  }
  .hero {
    padding: 40px 20px 32px;
  }
  .hero-title {
    font-size: 1.625rem;
  }
}

/* === Auto Theme Button === */
.icon-btn#theme-auto.active {
  background: var(--brand-primary);
  color: var(--text-inverse);
  border-color: var(--brand-primary);
}

/* === Search Dropdown === */
.search-dropdown {
  position: absolute;
  top: calc(100% + 4px);
  left: 0;
  right: 0;
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  z-index: 300;
  max-height: 320px;
  overflow-y: auto;
  opacity: 0;
  transform: translateY(-4px);
  pointer-events: none;
  transition: all var(--transition-fast);
}
.search-dropdown.show {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}
.search-result {
  display: block;
  padding: 10px 14px;
  border-bottom: 1px solid var(--border-divider);
  text-decoration: none;
  color: inherit;
  transition: background var(--transition-fast);
}
.search-result:last-child {
  border-bottom: none;
}
.search-result:hover {
  background: var(--bg-hover);
}
.search-result-title {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 3px;
}
.search-result-title mark {
  background: var(--brand-light);
  color: var(--brand-primary);
  border-radius: 3px;
  padding: 0 2px;
  font-weight: 700;
}
.search-result-meta {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  line-height: 1.4;
}
.search-result-meta mark {
  background: transparent;
  color: var(--brand-primary);
  font-weight: 600;
}
.search-result-tag {
  display: inline-block;
  padding: 1px 6px;
  border-radius: 100px;
  background: var(--brand-light);
  color: var(--brand-primary);
  font-size: 0.6875rem;
  font-weight: 600;
  margin-right: 6px;
}
.search-empty {
  padding: 16px;
  text-align: center;
  font-size: 0.875rem;
  color: var(--text-tertiary);
}

/* ─── Sidebar TOC (二级目录) ─── */
.sidebar-toc-divider {
  height: 1px;
  background: var(--border-divider);
  margin: 8px 12px;
  opacity: 0.6;
}
.sidebar-toc-link {
  display: flex;
  align-items: flex-start;
  gap: 6px;
  padding: 4px 12px 4px 28px;
  font-size: 0.78rem;
  line-height: 1.45;
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: background var(--transition-fast), color var(--transition-fast);
  position: relative;
}
.sidebar-toc-link:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}
.sidebar-toc-link.active {
  color: var(--brand-primary);
  font-weight: 600;
  background: var(--brand-light);
}
.sidebar-toc-dot {
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--border-default);
  margin-top: 7px;
  flex-shrink: 0;
}
.sidebar-toc-link.active .sidebar-toc-dot {
  background: var(--brand-primary);
}
.sidebar-toc-link.sidebar-toc-h3 {
  font-size: 0.74rem;
  padding-left: 36px;
  color: var(--text-tertiary);
}
.sidebar-toc-link.sidebar-toc-h3 .sidebar-toc-dot {
  width: 3px;
  height: 3px;
  margin-top: 8px;
}
.sidebar-toc-link.sidebar-toc-h3:hover {
  color: var(--text-secondary);
}