/* ============================================================
   Ceramic Materials Knowledge Base v2.0
   Advanced Ceramic Materials Research Database
   Design: High-tech glassmorphism + academic professionalism
   ============================================================ */

/* --- CSS Variables (Dark Theme - Default) --- */
:root {
  /* Layout */
  --sidebar-width: 360px;
  --sidebar-collapsed: 0px;
  --header-height: 60px;
  --footer-height: 48px;
  --radius-sm: 6px;
  --radius: 10px;
  --radius-lg: 16px;
  --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.4s cubic-bezier(0.4, 0, 0.2, 1);

  /* Sidebar - Deep tech dark */
  --sidebar-bg: linear-gradient(180deg, #0a0e1a 0%, #0f1729 40%, #0d1525 100%);
  --sidebar-bg-solid: #0a0e1a;
  --sidebar-hover: rgba(30, 60, 114, 0.35);
  --sidebar-active: rgba(20, 80, 120, 0.4);
  --sidebar-text: #8da0b8;
  --sidebar-text-active: #ffffff;
  --sidebar-section-bg: rgba(255, 255, 255, 0.03);
  --sidebar-border: rgba(255, 255, 255, 0.06);
  --sidebar-search-bg: rgba(255, 255, 255, 0.05);
  --sidebar-search-border: rgba(255, 255, 255, 0.08);

  /* Accent colors - Vibrant tech palette */
  --accent: #00d4aa;
  --accent-glow: rgba(0, 212, 170, 0.3);
  --accent-2: #0ea5e9;
  --accent-2-glow: rgba(14, 165, 233, 0.25);
  --accent-3: #8b5cf6;
  --accent-3-glow: rgba(139, 92, 246, 0.2);
  --accent-warm: #f59e0b;
  --accent-warm-glow: rgba(245, 158, 11, 0.2);
  --accent-danger: #ef4444;
  --accent-success: #22c55e;

  /* Content area */
  --content-bg: #0d1117;
  --content-bg-2: #111827;
  --card-bg: rgba(22, 27, 34, 0.8);
  --card-bg-solid: #161b22;
  --card-hover: rgba(30, 38, 50, 0.9);
  --card-border: rgba(255, 255, 255, 0.06);
  --card-border-hover: rgba(0, 212, 170, 0.3);

  /* Text */
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --text-muted: #6e7681;
  --text-heading: #f0f6fc;
  --text-link: #58a6ff;
  --text-link-hover: #79c0ff;

  /* UI Elements */
  --border: rgba(255, 255, 255, 0.08);
  --border-strong: rgba(255, 255, 255, 0.12);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
  --shadow: 0 4px 16px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.5);
  --shadow-glow: 0 0 24px rgba(0, 212, 170, 0.15);

  /* Tags & Badges */
  --tag-bg: rgba(0, 212, 170, 0.08);
  --tag-text: #00d4aa;
  --tag-border: rgba(0, 212, 170, 0.2);
  --badge-bg: rgba(14, 165, 233, 0.1);
  --badge-text: #38bdf8;

  /* Code & References */
  --code-bg: rgba(0, 0, 0, 0.3);
  --code-text: #e6edf3;
  --ref-bg: rgba(14, 165, 233, 0.06);
  --ref-hover: rgba(14, 165, 233, 0.12);
  --ref-border: rgba(14, 165, 233, 0.15);

  /* Highlights */
  --highlight-bg: rgba(0, 212, 170, 0.08);
  --highlight-text: #00d4aa;
  --mark-bg: rgba(245, 158, 11, 0.12);
  --mark-text: #fbbf24;

  /* Tab & Navigation */
  --tab-bg: transparent;
  --tab-hover: rgba(255, 255, 255, 0.04);
  --tab-active: rgba(0, 212, 170, 0.1);
  --tab-active-border: #00d4aa;

  /* Overlay */
  --overlay-bg: rgba(0, 0, 0, 0.6);
  --overlay-blur: 8px;

  /* Glass effect */
  --glass-bg: rgba(22, 27, 34, 0.7);
  --glass-border: rgba(255, 255, 255, 0.08);
  --glass-blur: 12px;

  /* Gradient accents */
  --gradient-tech: linear-gradient(135deg, #00d4aa 0%, #0ea5e9 50%, #8b5cf6 100%);
  --gradient-accent: linear-gradient(135deg, #00d4aa 0%, #0ea5e9 100%);
  --gradient-warm: linear-gradient(135deg, #f59e0b 0%, #ef4444 100%);
  --gradient-dark: linear-gradient(180deg, #0d1117 0%, #161b22 100%);
}

/* --- Light Theme --- */
body.light-theme {
  --sidebar-bg: linear-gradient(180deg, #f8fafc 0%, #f1f5f9 40%, #f8fafc 100%);
  --sidebar-bg-solid: #f8fafc;
  --sidebar-hover: rgba(0, 212, 170, 0.08);
  --sidebar-active: rgba(0, 212, 170, 0.12);
  --sidebar-text: #475569;
  --sidebar-text-active: #0f172a;
  --sidebar-section-bg: rgba(0, 0, 0, 0.02);
  --sidebar-border: rgba(0, 0, 0, 0.06);
  --sidebar-search-bg: rgba(0, 0, 0, 0.03);
  --sidebar-search-border: rgba(0, 0, 0, 0.08);

  --content-bg: #f0f2f5;
  --content-bg-2: #ffffff;
  --card-bg: rgba(255, 255, 255, 0.85);
  --card-bg-solid: #ffffff;
  --card-hover: rgba(248, 250, 252, 0.95);
  --card-border: rgba(0, 0, 0, 0.06);
  --card-border-hover: rgba(0, 212, 170, 0.3);

  --text-primary: #1e293b;
  --text-secondary: #64748b;
  --text-muted: #94a3b8;
  --text-heading: #0f172a;
  --text-link: #0284c7;
  --text-link-hover: #0ea5e9;

  --border: rgba(0, 0, 0, 0.08);
  --border-strong: rgba(0, 0, 0, 0.12);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06);
  --shadow: 0 4px 16px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.12);
  --shadow-glow: 0 0 24px rgba(0, 212, 170, 0.1);

  --tag-bg: rgba(0, 212, 170, 0.08);
  --tag-text: #0d9488;
  --badge-bg: rgba(14, 165, 233, 0.08);
  --badge-text: #0284c7;

  --code-bg: rgba(0, 0, 0, 0.04);
  --code-text: #1e293b;
  --ref-bg: rgba(14, 165, 233, 0.04);
  --ref-hover: rgba(14, 165, 233, 0.08);
  --ref-border: rgba(14, 165, 233, 0.1);

  --highlight-bg: rgba(0, 212, 170, 0.06);
  --highlight-text: #0d9488;
  --mark-bg: rgba(245, 158, 11, 0.08);
  --mark-text: #d97706;

  --tab-hover: rgba(0, 0, 0, 0.03);
  --tab-active: rgba(0, 212, 170, 0.06);

  --overlay-bg: rgba(0, 0, 0, 0.3);
  --glass-bg: rgba(255, 255, 255, 0.7);
  --glass-border: rgba(0, 0, 0, 0.06);
  --gradient-dark: linear-gradient(180deg, #f8fafc 0%, #f1f5f9 100%);
}

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

html {
  font-size: 15px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", "Helvetica Neue", sans-serif;
  background: var(--content-bg);
  color: var(--text-primary);
  line-height: 1.7;
  display: flex;
  min-height: 100vh;
  overflow-x: hidden;
  transition: background var(--transition), color var(--transition);
}

/* --- Custom Scrollbar --- */
::-webkit-scrollbar { width: 7px; height: 7px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb {
  background: rgba(128, 128, 128, 0.3);
  border-radius: 4px;
  transition: background var(--transition);
}
::-webkit-scrollbar-thumb:hover { background: rgba(128, 128, 128, 0.5); }
.sidebar ::-webkit-scrollbar-thumb { background: rgba(255, 255, 255, 0.1); }
.sidebar ::-webkit-scrollbar-thumb:hover { background: rgba(255, 255, 255, 0.2); }

/* --- Selection --- */
::selection { background: rgba(0, 212, 170, 0.25); color: var(--text-heading); }

/* ============================================================
   SIDEBAR
   ============================================================ */
.sidebar {
  width: var(--sidebar-width);
  min-width: var(--sidebar-width);
  height: 100vh;
  position: sticky;
  top: 0;
  background: var(--sidebar-bg);
  border-right: 1px solid var(--sidebar-border);
  display: flex;
  flex-direction: column;
  z-index: 100;
  transition: transform var(--transition), width var(--transition);
  overflow: hidden;
}

/* Sidebar Header */
.sidebar-header {
  padding: 18px 20px 14px;
  border-bottom: 1px solid var(--sidebar-border);
  background: rgba(0, 0, 0, 0.15);
  position: relative;
}

.sidebar-header::after {
  content: '';
  position: absolute;
  bottom: -1px;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--accent), transparent);
  opacity: 0.5;
}

.sidebar-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 6px;
}

.sidebar-logo svg {
  width: 28px;
  height: 28px;
  flex-shrink: 0;
}

.sidebar-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--sidebar-text-active);
  letter-spacing: -0.3px;
  background: var(--gradient-accent);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.sidebar-subtitle {
  font-size: 0.72rem;
  color: var(--sidebar-text);
  opacity: 0.7;
  letter-spacing: 0.3px;
}

/* Sidebar Search */
.sidebar-search {
  padding: 12px 16px;
  border-bottom: 1px solid var(--sidebar-border);
}

.search-wrapper {
  position: relative;
}

.search-input {
  width: 100%;
  padding: 8px 12px 8px 34px;
  background: var(--sidebar-search-bg);
  border: 1px solid var(--sidebar-search-border);
  border-radius: var(--radius-sm);
  color: var(--sidebar-text-active);
  font-size: 0.85rem;
  outline: none;
  transition: all var(--transition);
}

.search-input::placeholder { color: var(--sidebar-text); opacity: 0.6; }

.search-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
  background: rgba(255, 255, 255, 0.08);
}

.search-icon {
  position: absolute;
  left: 10px;
  top: 50%;
  transform: translateY(-50%);
  width: 16px;
  height: 16px;
  color: var(--sidebar-text);
  opacity: 0.5;
  pointer-events: none;
}

.search-clear {
  position: absolute;
  right: 8px;
  top: 50%;
  transform: translateY(-50%);
  background: none;
  border: none;
  color: var(--sidebar-text);
  cursor: pointer;
  font-size: 1rem;
  opacity: 0;
  transition: opacity var(--transition);
  padding: 2px 6px;
}
.search-wrapper.has-text .search-clear { opacity: 0.6; }
.search-clear:hover { opacity: 1; }

/* Sidebar Tree Navigation */
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  overflow-x: hidden;
  padding: 8px 0;
}

.nav-section {
  margin-bottom: 2px;
}

.nav-section-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 16px 8px;
  cursor: pointer;
  user-select: none;
  transition: background var(--transition);
}

.nav-section-header:hover {
  background: var(--sidebar-hover);
}

.nav-section-icon {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 4px;
  font-size: 0.75rem;
}

.nav-section-title {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--sidebar-text);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.nav-section-count {
  font-size: 0.7rem;
  color: var(--text-muted);
  background: var(--sidebar-section-bg);
  padding: 1px 7px;
  border-radius: 10px;
  border: 1px solid var(--sidebar-border);
}

.nav-section-toggle {
  width: 14px;
  height: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--sidebar-text);
  opacity: 0.5;
  transition: transform var(--transition);
  flex-shrink: 0;
}

.nav-section.expanded .nav-section-toggle {
  transform: rotate(90deg);
}

.nav-section-children {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
}

.nav-section.expanded .nav-section-children {
  max-height: 5000px;
}

/* Nav Items (Materials) */
.nav-item {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 7px 16px 7px 40px;
  cursor: pointer;
  user-select: none;
  transition: all var(--transition);
  position: relative;
  border-left: 2px solid transparent;
}

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

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

.nav-item.active .nav-item-label {
  color: var(--sidebar-text-active);
  font-weight: 600;
}

.nav-item-bullet {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--text-muted);
  flex-shrink: 0;
  transition: all var(--transition);
}

.nav-item:hover .nav-item-bullet,
.nav-item.active .nav-item-bullet {
  background: var(--accent);
  box-shadow: 0 0 8px var(--accent-glow);
}

.nav-item-label {
  font-size: 0.82rem;
  color: var(--sidebar-text);
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  transition: color var(--transition);
}

.nav-item-filecount {
  font-size: 0.68rem;
  color: var(--text-muted);
  opacity: 0.6;
  flex-shrink: 0;
}

/* Nav Sub Items (Sections) */
.nav-sublist {
  margin-left: 40px;
  border-left: 1px solid var(--sidebar-border);
  padding-left: 0;
}

.nav-sub-item {
  display: flex;
  align-items: center;
  gap: 5px;
  padding: 5px 12px 5px 14px;
  cursor: pointer;
  user-select: none;
  font-size: 0.76rem;
  color: var(--sidebar-text);
  opacity: 0.8;
  transition: all var(--transition);
  position: relative;
}

.nav-sub-item::before {
  content: '';
  position: absolute;
  left: -1px;
  top: 50%;
  width: 8px;
  height: 1px;
  background: var(--sidebar-border);
}

.nav-sub-item:hover {
  color: var(--sidebar-text-active);
  background: var(--sidebar-hover);
}

.nav-sub-item.active {
  color: var(--accent);
  font-weight: 500;
}

.nav-sub-item-icon {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
  opacity: 0.6;
}

/* Search Results */
.search-results {
  padding: 4px 0;
}

.search-result-item {
  padding: 8px 16px 8px 20px;
  cursor: pointer;
  border-left: 2px solid transparent;
  transition: all var(--transition);
}

.search-result-item:hover {
  background: var(--sidebar-hover);
  border-left-color: var(--accent);
}

.search-result-category {
  font-size: 0.68rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.3px;
  margin-bottom: 2px;
}

.search-result-label {
  font-size: 0.82rem;
  color: var(--sidebar-text);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.search-result-item:hover .search-result-label {
  color: var(--sidebar-text-active);
}

.search-highlight {
  background: var(--tag-bg);
  color: var(--accent);
  padding: 0 2px;
  border-radius: 2px;
}

.no-results {
  padding: 20px;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.85rem;
}

/* Sidebar Footer */
.sidebar-footer {
  padding: 10px 16px;
  border-top: 1px solid var(--sidebar-border);
  background: rgba(0, 0, 0, 0.1);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

.sidebar-stats {
  display: flex;
  gap: 12px;
  font-size: 0.7rem;
  color: var(--sidebar-text);
  opacity: 0.6;
}

.sidebar-stat {
  display: flex;
  align-items: center;
  gap: 3px;
}

.sidebar-stat-value {
  color: var(--accent);
  font-weight: 600;
}

/* Theme Toggle */
.theme-toggle {
  background: var(--sidebar-search-bg);
  border: 1px solid var(--sidebar-border);
  border-radius: var(--radius-sm);
  padding: 5px 10px;
  cursor: pointer;
  color: var(--sidebar-text);
  font-size: 0.72rem;
  display: flex;
  align-items: center;
  gap: 5px;
  transition: all var(--transition);
}

.theme-toggle:hover {
  background: var(--sidebar-hover);
  color: var(--sidebar-text-active);
}

.theme-toggle svg {
  width: 14px;
  height: 14px;
}

/* ============================================================
   MAIN CONTENT
   ============================================================ */
.main-content {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* Top Bar */
.top-bar {
  height: var(--header-height);
  background: var(--glass-bg);
  backdrop-filter: blur(var(--glass-blur));
  -webkit-backdrop-filter: blur(var(--glass-blur));
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  padding: 0 24px;
  gap: 16px;
  position: sticky;
  top: 0;
  z-index: 50;
  transition: background var(--transition);
}

.sidebar-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 6px 8px;
  cursor: pointer;
  color: var(--text-secondary);
  display: none;
  align-items: center;
  justify-content: center;
  transition: all var(--transition);
}

.sidebar-toggle:hover {
  background: var(--tab-hover);
  color: var(--text-primary);
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  flex: 1;
  min-width: 0;
  font-size: 0.82rem;
}

.breadcrumb-item {
  color: var(--text-secondary);
  white-space: nowrap;
  cursor: pointer;
  transition: color var(--transition);
}

.breadcrumb-item:hover { color: var(--text-link); }
.breadcrumb-item.current { color: var(--text-primary); font-weight: 500; }

.breadcrumb-separator {
  color: var(--text-muted);
  font-size: 0.7rem;
}

.top-bar-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.top-bar-btn {
  background: var(--tab-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 6px 10px;
  cursor: pointer;
  color: var(--text-secondary);
  font-size: 0.78rem;
  display: flex;
  align-items: center;
  gap: 5px;
  transition: all var(--transition);
}

.top-bar-btn:hover {
  background: var(--tab-hover);
  color: var(--text-primary);
  border-color: var(--border-strong);
}

.top-bar-btn svg {
  width: 14px;
  height: 14px;
}

/* Content Area */
.content-area {
  flex: 1;
  padding: 32px 40px;
  max-width: 1400px;
  width: 100%;
  margin: 0 auto;
}

/* ============================================================
   WELCOME VIEW
   ============================================================ */
.welcome-view {
  animation: fadeInUp 0.5s ease;
}

.welcome-hero {
  text-align: center;
  padding: 60px 20px 48px;
  position: relative;
  overflow: hidden;
}

.welcome-hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -10%;
  right: -10%;
  height: 200%;
  background: radial-gradient(ellipse at center, var(--accent-glow) 0%, transparent 60%);
  opacity: 0.3;
  pointer-events: none;
}

.welcome-hero-icon {
  width: 80px;
  height: 80px;
  margin: 0 auto 20px;
  position: relative;
}

.welcome-hero-title {
  font-size: 2.4rem;
  font-weight: 800;
  letter-spacing: -1px;
  margin-bottom: 12px;
  background: var(--gradient-tech);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  position: relative;
}

.welcome-hero-desc {
  font-size: 1.05rem;
  color: var(--text-secondary);
  max-width: 640px;
  margin: 0 auto;
  line-height: 1.8;
}

.welcome-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 16px;
  margin: 36px 0;
}

.stat-card {
  background: var(--card-bg);
  backdrop-filter: blur(8px);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 20px;
  text-align: center;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.stat-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--gradient-accent);
  opacity: 0;
  transition: opacity var(--transition);
}

.stat-card:hover {
  border-color: var(--card-border-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.stat-card:hover::before { opacity: 1; }

.stat-value {
  font-size: 2rem;
  font-weight: 800;
  background: var(--gradient-accent);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.2;
}

.stat-label {
  font-size: 0.78rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-top: 4px;
}

/* Category Grid */
.section-title {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--text-heading);
  margin: 40px 0 20px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.section-title::before {
  content: '';
  width: 4px;
  height: 20px;
  background: var(--gradient-accent);
  border-radius: 2px;
}

.category-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
  margin-bottom: 40px;
}

.category-card {
  background: var(--card-bg);
  backdrop-filter: blur(8px);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 24px;
  cursor: pointer;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.category-card::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--gradient-accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--transition-slow);
}

.category-card:hover {
  border-color: var(--card-border-hover);
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg), var(--shadow-glow);
}

.category-card:hover::after { transform: scaleX(1); }

.category-card-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  margin-bottom: 14px;
  background: var(--tag-bg);
  border: 1px solid var(--tag-border);
}

.category-card-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-heading);
  margin-bottom: 6px;
}

.category-card-desc {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 12px;
}

.category-card-meta {
  display: flex;
  gap: 12px;
  font-size: 0.75rem;
  color: var(--text-muted);
}

.category-card-meta span {
  display: flex;
  align-items: center;
  gap: 4px;
}

.category-card-arrow {
  position: absolute;
  top: 24px;
  right: 24px;
  color: var(--text-muted);
  opacity: 0;
  transform: translateX(-8px);
  transition: all var(--transition);
}

.category-card:hover .category-card-arrow {
  opacity: 1;
  transform: translateX(0);
  color: var(--accent);
}

/* ============================================================
   MATERIAL DETAIL VIEW
   ============================================================ */
.material-view {
  animation: fadeInUp 0.4s ease;
}

.material-header {
  margin-bottom: 28px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--border);
}

.material-header-top {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 16px;
}

.material-icon {
  width: 56px;
  height: 56px;
  border-radius: var(--radius);
  background: var(--gradient-accent);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  flex-shrink: 0;
  box-shadow: 0 4px 16px var(--accent-glow);
}

.material-title {
  font-size: 1.8rem;
  font-weight: 800;
  color: var(--text-heading);
  letter-spacing: -0.5px;
  line-height: 1.3;
}

.material-subtitle {
  font-size: 0.9rem;
  color: var(--text-secondary);
  margin-top: 4px;
}

.material-summary {
  font-size: 0.92rem;
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: 16px;
}

/* Quick Facts */
.quick-facts {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 12px;
  margin-top: 16px;
}

.quick-fact {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--radius-sm);
  padding: 10px 14px;
  display: flex;
  align-items: center;
  gap: 10px;
  transition: all var(--transition);
}

.quick-fact:hover {
  border-color: var(--card-border-hover);
  background: var(--card-hover);
}

.quick-fact-icon {
  width: 32px;
  height: 32px;
  border-radius: 6px;
  background: var(--tag-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.9rem;
  flex-shrink: 0;
}

.quick-fact-content {
  flex: 1;
  min-width: 0;
}

.quick-fact-label {
  font-size: 0.68rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.3px;
}

.quick-fact-value {
  font-size: 0.82rem;
  color: var(--text-primary);
  font-weight: 600;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* Section Tabs */
.section-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 24px;
  border-bottom: 1px solid var(--border);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.section-tab {
  padding: 10px 18px;
  cursor: pointer;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-secondary);
  border: none;
  background: transparent;
  position: relative;
  transition: all var(--transition);
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 6px;
}

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

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

.section-tab.active::after {
  content: '';
  position: absolute;
  bottom: -1px;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--accent);
  border-radius: 1px 1px 0 0;
}

.section-tab-icon {
  width: 15px;
  height: 15px;
  opacity: 0.7;
}

.section-tab.active .section-tab-icon { opacity: 1; }

/* Content Cards */
.content-card {
  background: var(--card-bg);
  backdrop-filter: blur(8px);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  padding: 28px;
  margin-bottom: 20px;
  transition: all var(--transition);
  animation: fadeInUp 0.3s ease;
}

.content-card:hover {
  border-color: var(--card-border-hover);
  box-shadow: var(--shadow);
}

.content-card-header {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 16px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}

.content-card-icon {
  width: 28px;
  height: 28px;
  border-radius: 6px;
  background: var(--tag-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  flex-shrink: 0;
}

.content-card-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-heading);
  flex: 1;
}

.content-card-body {
  font-size: 0.9rem;
  color: var(--text-primary);
  line-height: 1.85;
}

.content-card-body p {
  margin-bottom: 12px;
}

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

.content-card-body strong {
  color: var(--text-heading);
  font-weight: 600;
}

.content-card-body em {
  color: var(--accent);
  font-style: normal;
  font-weight: 500;
}

.content-card-body ul, .content-card-body ol {
  margin: 8px 0 12px 20px;
}

.content-card-body li {
  margin-bottom: 6px;
}

.content-card-body code {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.82rem;
  font-family: "SF Mono", "Fira Code", "Consolas", monospace;
}

.content-card-body mark {
  background: var(--mark-bg);
  color: var(--mark-text);
  padding: 1px 4px;
  border-radius: 3px;
}

/* References */
.references {
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px dashed var(--border);
}

.references-title {
  font-size: 0.78rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.3px;
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 5px;
}

.reference-item {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  padding: 8px 12px;
  background: var(--ref-bg);
  border: 1px solid var(--ref-border);
  border-radius: var(--radius-sm);
  margin-bottom: 6px;
  font-size: 0.78rem;
  color: var(--text-secondary);
  transition: all var(--transition);
  cursor: pointer;
  position: relative;
}

.reference-item:hover {
  background: var(--ref-hover);
  color: var(--text-primary);
  border-color: var(--accent);
  transform: translateX(4px);
  box-shadow: 0 4px 12px rgba(77, 166, 255, 0.15);
}

.reference-item:hover .reference-wechat-hint {
  opacity: 1;
  transform: translateX(0);
}

.reference-number {
  color: var(--accent);
  font-weight: 600;
  flex-shrink: 0;
}

.reference-text {
  flex: 1;
  word-break: break-all;
}

.reference-wechat-hint {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  flex-shrink: 0;
  padding: 2px 8px;
  font-size: 0.7rem;
  font-weight: 500;
  color: #fff;
  background: linear-gradient(135deg, #07c160, #00a854);
  border-radius: 8px;
  opacity: 0;
  transform: translateX(-6px);
  transition: all var(--transition);
  white-space: nowrap;
}

.reference-wechat-hint::before {
  content: "💬";
  font-size: 0.75rem;
}

/* Tags */
.tag-container {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 12px;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  background: var(--tag-bg);
  color: var(--tag-text);
  border: 1px solid var(--tag-border);
  border-radius: 12px;
  font-size: 0.72rem;
  font-weight: 500;
}

.tag-badge {
  background: var(--badge-bg);
  color: var(--badge-text);
  border: 1px solid rgba(14, 165, 233, 0.2);
}

/* Info Banner */
.info-banner {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  background: var(--highlight-bg);
  border: 1px solid var(--tag-border);
  border-radius: var(--radius-sm);
  margin-bottom: 20px;
  font-size: 0.85rem;
  color: var(--highlight-text);
}

.info-banner svg {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
}

/* Back to Top */
.back-to-top {
  position: fixed;
  bottom: 32px;
  right: 32px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--glass-bg);
  backdrop-filter: blur(var(--glass-blur));
  border: 1px solid var(--border-strong);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text-secondary);
  opacity: 0;
  transform: translateY(20px);
  transition: all var(--transition);
  z-index: 90;
  box-shadow: var(--shadow);
}

.back-to-top.visible {
  opacity: 1;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  box-shadow: var(--shadow-glow);
}

.back-to-top svg {
  width: 20px;
  height: 20px;
}

/* Loading Spinner */
.loading-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 80px 20px;
  gap: 16px;
}

.loading-spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

.loading-text {
  color: var(--text-muted);
  font-size: 0.85rem;
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 60px 20px;
  color: var(--text-muted);
}

.empty-state-icon {
  width: 60px;
  height: 60px;
  margin: 0 auto 16px;
  opacity: 0.3;
}

.empty-state-text {
  font-size: 0.9rem;
}

/* ============================================================
   ANIMATIONS
   ============================================================ */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

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

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

@keyframes shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

/* ============================================================
   WECHAT QR MODAL (Reference Click Popup)
   ============================================================ */
.wechat-modal {
  position: fixed;
  inset: 0;
  z-index: 10000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.wechat-modal.active {
  display: flex;
}

.wechat-modal-backdrop {
  position: absolute;
  inset: 0;
  background: rgba(0, 0, 0, 0.78);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  animation: modalBackdropIn 0.3s ease-out;
}

@keyframes modalBackdropIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.wechat-modal-content {
  position: relative;
  max-width: 440px;
  width: 100%;
  background: linear-gradient(145deg, var(--bg-card), var(--bg-secondary));
  border: 1px solid var(--border);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 30px 80px rgba(0, 0, 0, 0.5),
              0 0 0 1px rgba(7, 193, 96, 0.15);
  animation: modalContentIn 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
  max-height: 90vh;
  overflow-y: auto;
}

@keyframes modalContentIn {
  from { opacity: 0; transform: scale(0.85) translateY(20px); }
  to   { opacity: 1; transform: scale(1) translateY(0); }
}

.wechat-modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px 22px;
  background: linear-gradient(135deg, #07c160 0%, #00a854 100%);
  color: #fff;
}

.wechat-modal-header-title {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  font-size: 1rem;
}

.wechat-modal-header-title svg {
  flex-shrink: 0;
}

.wechat-modal-close {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: none;
  background: rgba(255, 255, 255, 0.15);
  color: #fff;
  border-radius: 50%;
  cursor: pointer;
  font-size: 18px;
  line-height: 1;
  transition: all 0.2s ease;
}

.wechat-modal-close:hover {
  background: rgba(255, 255, 255, 0.3);
  transform: rotate(90deg);
}

.wechat-modal-body {
  padding: 24px 22px;
  text-align: center;
}

.wechat-modal-ref-wrapper {
  margin-bottom: 18px;
  padding: 12px 14px;
  background: rgba(7, 193, 96, 0.08);
  border-left: 3px solid #07c160;
  border-radius: 6px;
  text-align: left;
}

.wechat-modal-ref-label {
  display: block;
  font-size: 0.72rem;
  font-weight: 600;
  color: #07c160;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  margin-bottom: 4px;
}

.wechat-modal-ref {
  display: block;
  font-size: 0.85rem;
  color: var(--text-secondary);
  word-break: break-all;
  font-family: 'Consolas', 'Monaco', monospace;
  line-height: 1.4;
}

.wechat-modal-image-wrapper {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 0 auto 16px;
  width: 260px;
  height: 333px;
  border-radius: 10px;
  overflow: hidden;
  background: #fff;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.2);
  position: relative;
}

.wechat-modal-image {
  width: 100%;
  height: 100%;
  object-fit: contain;
  display: block;
}

.wechat-modal-scan-tip {
  position: absolute;
  bottom: -10px;
  left: 50%;
  transform: translateX(-50%);
  background: #07c160;
  color: #fff;
  padding: 3px 12px;
  border-radius: 10px;
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.5px;
  white-space: nowrap;
}

.wechat-modal-instruction {
  margin-top: 22px;
  padding: 14px 16px;
  background: rgba(77, 166, 255, 0.06);
  border: 1px dashed rgba(77, 166, 255, 0.3);
  border-radius: 8px;
  text-align: left;
}

.wechat-modal-instruction-title {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 8px;
}

.wechat-modal-instruction-text {
  font-size: 0.82rem;
  line-height: 1.65;
  color: var(--text-secondary);
}

.wechat-modal-instruction-text strong {
  color: #07c160;
  font-weight: 600;
}

.wechat-modal-footer {
  padding: 14px 22px 18px;
  text-align: center;
  font-size: 0.75rem;
  color: var(--text-muted);
  border-top: 1px solid var(--border);
  background: rgba(0, 0, 0, 0.05);
}

@media (max-width: 480px) {
  .wechat-modal-content { max-width: 100%; }
  .wechat-modal-image-wrapper { width: 220px; height: 282px; }
  .wechat-modal-header, .wechat-modal-body, .wechat-modal-footer { padding-left: 16px; padding-right: 16px; }
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 1024px) {
  :root { --sidebar-width: 300px; }
  .content-area { padding: 24px 28px; }
  .welcome-hero-title { font-size: 2rem; }
}

@media (max-width: 768px) {
  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    transform: translateX(-100%);
    box-shadow: var(--shadow-lg);
  }

  .sidebar.open { transform: translateX(0); }

  .sidebar-toggle { display: flex; }

  .content-area { padding: 20px 16px; }

  .welcome-hero { padding: 40px 16px 32px; }
  .welcome-hero-title { font-size: 1.6rem; }
  .welcome-hero-desc { font-size: 0.9rem; }

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

  .material-title { font-size: 1.4rem; }
  .material-header-top { flex-direction: column; gap: 12px; }

  .quick-facts { grid-template-columns: 1fr 1fr; }

  .content-card { padding: 20px 16px; }

  .section-tabs { gap: 2px; }
  .section-tab { padding: 8px 12px; font-size: 0.8rem; }

  .back-to-top { bottom: 20px; right: 20px; }

  .top-bar { padding: 0 16px; }
}

@media (max-width: 480px) {
  .quick-facts { grid-template-columns: 1fr; }
  .welcome-stats { grid-template-columns: 1fr 1fr; }
  .stat-value { font-size: 1.5rem; }
}

/* Sidebar Overlay (Mobile) */
.sidebar-overlay {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: var(--overlay-bg);
  backdrop-filter: blur(var(--overlay-blur));
  z-index: 99;
  opacity: 0;
  transition: opacity var(--transition);
}

.sidebar-overlay.visible {
  display: block;
  opacity: 1;
}

/* Print */
@media print {
  .sidebar, .top-bar, .back-to-top, .sidebar-overlay { display: none !important; }
  .content-area { padding: 0; max-width: 100%; }
  .content-card { break-inside: avoid; border: 1px solid #ddd; }
}