/* ===== Algorithm Visualization Platform - Core Styles ===== */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* ===== CSS Custom Properties ===== */
:root {
  --font-sans: 'Inter', sans-serif;
  --font-mono: 'JetBrains Mono', monospace;

  /* Brand Colors */
  --orange-400: #fb923c;
  --orange-500: #f97316;
  --orange-600: #ea580c;
  --orange-glow: rgba(249, 115, 22, 0.25);

  /* Dark Mode (default) */
  --bg-primary: #0a0a0f;
  --bg-secondary: #111118;
  --bg-card: #16161f;
  --bg-card-hover: #1e1e2a;
  --bg-elevated: #1c1c28;
  --border-color: rgba(249, 115, 22, 0.15);
  --border-subtle: rgba(255, 255, 255, 0.06);
  --text-primary: #f1f1f5;
  --text-secondary: #9494a8;
  --text-muted: #5a5a72;
  --accent: #f97316;
  --accent-hover: #fb923c;
  --success: #22c55e;
  --warning: #eab308;
  --error: #ef4444;
  --info: #3b82f6;

  /* Gradients */
  --gradient-brand: linear-gradient(135deg, #f97316, #ea580c);
  --gradient-hero: radial-gradient(ellipse 80% 60% at 50% -20%, rgba(249,115,22,0.25) 0%, transparent 70%);
  --gradient-card: linear-gradient(145deg, rgba(249,115,22,0.08) 0%, rgba(26,26,40,0) 100%);
  --gradient-mesh: radial-gradient(at 40% 20%, rgba(249,115,22,0.12) 0px, transparent 50%), radial-gradient(at 80% 0%, rgba(234,88,12,0.08) 0px, transparent 50%), radial-gradient(at 0% 50%, rgba(249,115,22,0.05) 0px, transparent 50%);

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.5);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.5);
  --shadow-orange: 0 0 24px rgba(249,115,22,0.2);
  --shadow-orange-lg: 0 0 48px rgba(249,115,22,0.3);

  /* Sizes */
  --navbar-h: 64px;
  --sidebar-w: 260px;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;
}

/* Light Mode */
[data-theme="light"] {
  --bg-primary: #fafafa;
  --bg-secondary: #f4f4f8;
  --bg-card: #ffffff;
  --bg-card-hover: #f8f8fc;
  --bg-elevated: #ffffff;
  --border-color: rgba(249, 115, 22, 0.2);
  --border-subtle: rgba(0, 0, 0, 0.08);
  --text-primary: #0d0d14;
  --text-secondary: #4a4a6a;
  --text-muted: #8888a0;
  --gradient-hero: radial-gradient(ellipse 80% 60% at 50% -20%, rgba(249,115,22,0.15) 0%, transparent 70%);
  --gradient-card: linear-gradient(145deg, rgba(249,115,22,0.04) 0%, rgba(255,255,255,0) 100%);
  --gradient-mesh: radial-gradient(at 40% 20%, rgba(249,115,22,0.08) 0px, transparent 50%);
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.1);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.12);
  --shadow-orange: 0 0 24px rgba(249,115,22,0.15);
}

/* ===== Reset & Base ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; font-size: 16px; }
body {
  font-family: var(--font-sans);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  transition: background var(--transition-slow), color var(--transition-slow);
  overflow-x: hidden;
}
a { color: inherit; text-decoration: none; }
img { max-width: 100%; }
button { cursor: pointer; border: none; background: none; font-family: inherit; }
input, textarea, select { font-family: inherit; }

/* ===== Scrollbar ===== */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--bg-secondary); }
::-webkit-scrollbar-thumb { background: rgba(249,115,22,0.4); border-radius: var(--radius-full); }
::-webkit-scrollbar-thumb:hover { background: var(--accent); }

/* ===== Navbar ===== */
.navbar {
  position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
  height: var(--navbar-h);
  display: flex; align-items: center;
  padding: 0 24px;
  background: rgba(10, 10, 15, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  transition: background var(--transition-slow);
}
[data-theme="light"] .navbar {
  background: rgba(255, 255, 255, 0.85);
}
.navbar-brand {
  display: flex; align-items: center; gap: 10px;
  font-size: 1.2rem; font-weight: 800;
}
.navbar-brand .logo-icon {
  width: 36px; height: 36px;
  background: var(--gradient-brand);
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  font-size: 1rem;
  box-shadow: var(--shadow-orange);
}
.navbar-brand .logo-text { color: var(--text-primary); }
.navbar-brand .logo-text span { color: var(--accent); }
.navbar-links {
  display: flex; align-items: center; gap: 4px;
  margin-left: 32px;
}
.navbar-links a {
  padding: 6px 14px;
  border-radius: var(--radius-sm);
  font-size: 0.875rem; font-weight: 500;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}
.navbar-links a:hover, .navbar-links a.active {
  color: var(--text-primary);
  background: rgba(249,115,22,0.1);
}
.navbar-links a.active { color: var(--accent); }
.navbar-actions {
  margin-left: auto;
  display: flex; align-items: center; gap: 12px;
}
.theme-toggle {
  width: 36px; height: 36px;
  border-radius: var(--radius-sm);
  display: flex; align-items: center; justify-content: center;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  font-size: 1rem;
  transition: all var(--transition-fast);
}
.theme-toggle:hover { color: var(--accent); border-color: var(--border-color); }

/* Mobile Nav Toggle */
.nav-toggle {
  display: none; width: 36px; height: 36px;
  align-items: center; justify-content: center;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-primary); font-size: 1.2rem;
}
.mobile-menu {
  display: none;
  position: fixed; top: var(--navbar-h); left: 0; right: 0;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
  padding: 16px;
  z-index: 999;
  flex-direction: column; gap: 4px;
}
.mobile-menu.open { display: flex; }
.mobile-menu a {
  padding: 12px 16px;
  border-radius: var(--radius-sm);
  font-size: 0.9rem; font-weight: 500;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}
.mobile-menu a:hover { color: var(--text-primary); background: rgba(249,115,22,0.1); }

/* Bottom Nav (Mobile) */
.bottom-nav {
  display: none;
  position: fixed; bottom: 0; left: 0; right: 0;
  height: 64px;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  z-index: 999;
  align-items: center;
  justify-content: space-around;
  padding: 8px 0;
  backdrop-filter: blur(20px);
}
.bottom-nav-item {
  display: flex; flex-direction: column; align-items: center; gap: 3px;
  padding: 4px 16px;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.65rem; font-weight: 600;
  transition: all var(--transition-fast);
  text-transform: uppercase; letter-spacing: 0.5px;
}
.bottom-nav-item .nav-icon { font-size: 1.25rem; }
.bottom-nav-item.active { color: var(--accent); }

/* ===== Buttons ===== */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  font-size: 0.875rem; font-weight: 600;
  transition: all var(--transition-fast);
  white-space: nowrap;
}
.btn-primary {
  background: var(--gradient-brand);
  color: #fff;
  box-shadow: 0 4px 16px rgba(249,115,22,0.35);
}
.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(249,115,22,0.5);
}
.btn-primary:active { transform: translateY(0); }
.btn-secondary {
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  color: var(--text-primary);
}
.btn-secondary:hover {
  border-color: var(--border-color);
  background: var(--bg-card-hover);
}
.btn-outline {
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--accent);
}
.btn-outline:hover { background: rgba(249,115,22,0.1); }
.btn-sm { padding: 6px 14px; font-size: 0.8rem; }
.btn-lg { padding: 14px 28px; font-size: 1rem; border-radius: var(--radius-md); }
.btn-icon { width: 36px; height: 36px; padding: 0; border-radius: var(--radius-sm); }
.btn-icon-lg { width: 44px; height: 44px; padding: 0; border-radius: var(--radius-sm); }

/* ===== Cards ===== */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
  transition: all var(--transition-base);
}
.card:hover {
  border-color: var(--border-color);
  box-shadow: var(--shadow-orange);
  transform: translateY(-2px);
}
.card-glass {
  background: rgba(22, 22, 31, 0.7);
  backdrop-filter: blur(16px);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
}

/* ===== Algorithm Card ===== */
.algo-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}
.algo-card::before {
  content: '';
  position: absolute; top: 0; left: 0; right: 0; height: 2px;
  background: var(--gradient-brand);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--transition-base);
}
.algo-card:hover::before { transform: scaleX(1); }
.algo-card:hover {
  border-color: var(--border-color);
  box-shadow: var(--shadow-orange);
  transform: translateY(-3px);
}
.algo-card-icon {
  width: 48px; height: 48px;
  background: rgba(249,115,22,0.12);
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.4rem;
  margin-bottom: 14px;
  border: 1px solid rgba(249,115,22,0.2);
}
.algo-card-title {
  font-size: 1rem; font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 6px;
}
.algo-card-desc {
  font-size: 0.8rem;
  color: var(--text-secondary);
  line-height: 1.5;
  margin-bottom: 14px;
}
.algo-card-footer {
  display: flex; align-items: center; justify-content: space-between;
}

/* ===== Badges ===== */
.badge {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 3px 10px;
  border-radius: var(--radius-full);
  font-size: 0.72rem; font-weight: 600;
  letter-spacing: 0.3px;
  text-transform: uppercase;
}
.badge-easy { background: rgba(34,197,94,0.15); color: #22c55e; border: 1px solid rgba(34,197,94,0.25); }
.badge-medium { background: rgba(234,179,8,0.15); color: #eab308; border: 1px solid rgba(234,179,8,0.25); }
.badge-hard { background: rgba(239,68,68,0.15); color: #ef4444; border: 1px solid rgba(239,68,68,0.25); }
.badge-sorting { background: rgba(99,102,241,0.15); color: #818cf8; border: 1px solid rgba(99,102,241,0.25); }
.badge-searching { background: rgba(34,211,238,0.15); color: #22d3ee; border: 1px solid rgba(34,211,238,0.25); }
.badge-graph { background: rgba(168,85,247,0.15); color: #c084fc; border: 1px solid rgba(168,85,247,0.25); }
.badge-dp { background: rgba(249,115,22,0.15); color: #fb923c; border: 1px solid rgba(249,115,22,0.25); }
.badge-orange { background: rgba(249,115,22,0.15); color: var(--accent); border: 1px solid rgba(249,115,22,0.25); }

/* ===== Section Styles ===== */
.section { padding: 80px 0; }
.section-sm { padding: 48px 0; }
.container { max-width: 1200px; margin: 0 auto; padding: 0 24px; }
.container-lg { max-width: 1400px; margin: 0 auto; padding: 0 24px; }
.section-header { text-align: center; margin-bottom: 56px; }
.section-label {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 4px 14px;
  background: rgba(249,115,22,0.1);
  border: 1px solid rgba(249,115,22,0.2);
  border-radius: var(--radius-full);
  font-size: 0.78rem; font-weight: 600;
  color: var(--accent);
  letter-spacing: 0.5px;
  text-transform: uppercase;
  margin-bottom: 16px;
}
.section-title {
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -0.02em;
  margin-bottom: 16px;
}
.section-title span { color: var(--accent); }
.section-desc {
  font-size: 1.05rem;
  color: var(--text-secondary);
  max-width: 520px;
  margin: 0 auto;
  line-height: 1.6;
}

/* ===== Hero Section ===== */
.hero {
  min-height: 100vh;
  display: flex; align-items: center;
  position: relative;
  padding-top: var(--navbar-h);
  overflow: hidden;
}
.hero-bg {
  position: absolute; inset: 0;
  background: var(--gradient-hero);
  pointer-events: none;
}
.hero-grid {
  position: absolute; inset: 0;
  background-image: linear-gradient(rgba(249,115,22,0.04) 1px, transparent 1px), linear-gradient(90deg, rgba(249,115,22,0.04) 1px, transparent 1px);
  background-size: 40px 40px;
  pointer-events: none;
  mask-image: radial-gradient(ellipse 60% 50% at 50% 50%, black 0%, transparent 100%);
}
.hero-content { position: relative; z-index: 1; }
.hero-badge {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 6px 16px;
  background: rgba(249,115,22,0.1);
  border: 1px solid rgba(249,115,22,0.25);
  border-radius: var(--radius-full);
  font-size: 0.82rem; font-weight: 600;
  color: var(--accent);
  margin-bottom: 24px;
  animation: fadeInDown 0.6s ease;
}
.hero-title {
  font-size: clamp(2.5rem, 6vw, 4.5rem);
  font-weight: 900;
  line-height: 1.1;
  letter-spacing: -0.03em;
  margin-bottom: 20px;
  animation: fadeInUp 0.6s ease 0.1s backwards;
}
.hero-title span {
  background: var(--gradient-brand);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-subtitle {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 480px;
  line-height: 1.7;
  margin-bottom: 36px;
  animation: fadeInUp 0.6s ease 0.2s backwards;
}
.hero-actions {
  display: flex; align-items: center; gap: 14px; flex-wrap: wrap;
  animation: fadeInUp 0.6s ease 0.3s backwards;
}
.hero-stats {
  display: flex; align-items: center; gap: 32px;
  margin-top: 48px;
  animation: fadeInUp 0.6s ease 0.4s backwards;
}
.hero-stat-val {
  font-size: 1.8rem; font-weight: 800;
  color: var(--accent);
}
.hero-stat-label {
  font-size: 0.8rem; color: var(--text-muted);
  font-weight: 500;
}

/* Hero floating cards */
.hero-visual {
  position: relative;
}
.floating-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 16px 20px;
  box-shadow: var(--shadow-lg);
  animation: float 3s ease-in-out infinite;
}
.floating-card:nth-child(2) { animation-delay: -1.5s; }
.floating-card:nth-child(3) { animation-delay: -1s; }

/* ===== Visualization Canvas ===== */
.viz-container {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow: hidden;
}
.viz-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 16px 20px;
  border-bottom: 1px solid var(--border-subtle);
}
.viz-canvas-wrap {
  position: relative;
  background: var(--bg-secondary);
  padding: 20px;
  min-height: 280px;
  display: flex; align-items: flex-end; justify-content: center; gap: 4px;
}
canvas#vizCanvas {
  display: block;
  width: 100%;
  border-radius: var(--radius-sm);
}

/* Viz Controls */
.viz-controls {
  display: flex; align-items: center; gap: 10px;
  padding: 14px 20px;
  border-top: 1px solid var(--border-subtle);
  flex-wrap: wrap;
}
.speed-control { display: flex; align-items: center; gap: 8px; margin-left: auto; }
.speed-label { font-size: 0.78rem; color: var(--text-muted); font-weight: 500; }

/* Custom Range Slider */
input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100px; height: 4px;
  background: var(--bg-elevated);
  border-radius: var(--radius-full);
  outline: none;
}
input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 14px; height: 14px;
  background: var(--accent);
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 0 8px rgba(249,115,22,0.4);
}

/* Step Explanation Panel */
.step-panel {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
}
.step-panel-title {
  font-size: 0.78rem; font-weight: 700;
  color: var(--accent);
  text-transform: uppercase; letter-spacing: 0.5px;
  margin-bottom: 10px;
}
.step-panel-text {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
}
.step-indicator {
  display: flex; align-items: center; gap: 6px;
  margin-top: 12px;
}
.step-dot {
  width: 8px; height: 8px;
  border-radius: 50%;
  background: var(--border-subtle);
  transition: all var(--transition-fast);
}
.step-dot.active { background: var(--accent); transform: scale(1.3); }
.step-dot.done { background: var(--success); }

/* Code Panel */
.code-panel {
  background: #0d0d14;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow: hidden;
}
[data-theme="light"] .code-panel { background: #1a1a2e; }
.code-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 12px 16px;
  border-bottom: 1px solid rgba(255,255,255,0.06);
}
.code-dots { display: flex; gap: 6px; }
.code-dot {
  width: 10px; height: 10px;
  border-radius: 50%;
}
.code-dot:nth-child(1) { background: #ff5f56; }
.code-dot:nth-child(2) { background: #ffbd2e; }
.code-dot:nth-child(3) { background: #27c93f; }
.code-title { font-size: 0.78rem; color: #666; font-family: var(--font-mono); }
.code-body {
  padding: 20px;
  overflow-x: auto;
}
.code-body pre {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.7;
  color: #e2e8f0;
}
.code-line { display: flex; gap: 16px; padding: 1px 0; border-radius: 3px; }
.code-line.highlighted { background: rgba(249,115,22,0.15); margin: 0 -8px; padding: 1px 8px; }
.code-line-num { color: #444; min-width: 24px; text-align: right; user-select: none; }
.code-line-content { color: #e2e8f0; }
.kw { color: #c792ea; }
.fn { color: #82aaff; }
.str { color: #c3e88d; }
.num { color: #f78c6c; }
.cm { color: #546e7a; font-style: italic; }
.op { color: #89ddff; }

/* ===== Forms ===== */
.form-group { margin-bottom: 18px; }
.form-label {
  display: block;
  font-size: 0.82rem; font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 6px;
  letter-spacing: 0.2px;
}
.form-input {
  width: 100%;
  padding: 11px 14px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.9rem;
  transition: all var(--transition-fast);
  outline: none;
}
.form-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(249,115,22,0.12);
}
.form-input::placeholder { color: var(--text-muted); }
.form-select {
  width: 100%;
  padding: 11px 14px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.9rem;
  outline: none;
  cursor: pointer;
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='%23666'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M19 9l-7 7-7-7'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  background-size: 16px;
  padding-right: 36px;
}
.form-select:focus { border-color: var(--accent); }

/* ===== Tabs ===== */
.tabs { display: flex; gap: 4px; background: var(--bg-elevated); padding: 4px; border-radius: var(--radius-md); }
.tab-btn {
  flex: 1; padding: 8px 14px;
  border-radius: var(--radius-sm);
  font-size: 0.82rem; font-weight: 600;
  color: var(--text-muted);
  transition: all var(--transition-fast);
  text-align: center;
}
.tab-btn.active {
  background: var(--bg-card);
  color: var(--accent);
  box-shadow: var(--shadow-sm);
}
.tab-btn:hover:not(.active) { color: var(--text-primary); }

/* ===== Filter Chips ===== */
.filter-chips { display: flex; gap: 8px; flex-wrap: wrap; }
.chip {
  padding: 5px 14px;
  border-radius: var(--radius-full);
  font-size: 0.78rem; font-weight: 600;
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  transition: all var(--transition-fast);
  cursor: pointer;
  background: var(--bg-elevated);
}
.chip:hover { border-color: var(--border-color); color: var(--text-primary); }
.chip.active { background: rgba(249,115,22,0.15); border-color: rgba(249,115,22,0.4); color: var(--accent); }

/* ===== Search Bar ===== */
.search-bar {
  position: relative;
  max-width: 480px;
}
.search-bar input {
  width: 100%;
  padding: 12px 16px 12px 44px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 0.9rem;
  outline: none;
  transition: all var(--transition-fast);
}
.search-bar input:focus { border-color: var(--border-color); box-shadow: 0 0 0 3px rgba(249,115,22,0.1); }
.search-bar .search-icon {
  position: absolute; left: 14px; top: 50%; transform: translateY(-50%);
  color: var(--text-muted); pointer-events: none;
}

/* ===== Complexity Tags ===== */
.complexity-tag {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 3px 8px;
  background: rgba(249,115,22,0.08);
  border: 1px solid rgba(249,115,22,0.15);
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--accent);
}

/* ===== Progress & Stats ===== */
.progress-bar {
  height: 6px;
  background: var(--bg-elevated);
  border-radius: var(--radius-full);
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  background: var(--gradient-brand);
  border-radius: var(--radius-full);
  transition: width 0.8s ease;
}
.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
  text-align: center;
}
.stat-value { font-size: 2rem; font-weight: 800; color: var(--accent); }
.stat-label { font-size: 0.82rem; color: var(--text-muted); font-weight: 500; margin-top: 4px; }

/* ===== FAQ Accordion ===== */
.faq-item {
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}
.faq-item.open { border-color: var(--border-color); }
.faq-question {
  width: 100%;
  display: flex; align-items: center; justify-content: space-between;
  padding: 18px 20px;
  background: var(--bg-card);
  font-size: 0.95rem; font-weight: 600;
  color: var(--text-primary);
  text-align: left;
  transition: background var(--transition-fast);
}
.faq-question:hover { background: var(--bg-card-hover); }
.faq-icon { transition: transform var(--transition-fast); color: var(--accent); }
.faq-item.open .faq-icon { transform: rotate(180deg); }
.faq-answer {
  max-height: 0; overflow: hidden;
  transition: max-height 0.35s ease, padding 0.35s ease;
  padding: 0 20px;
  font-size: 0.9rem; color: var(--text-secondary); line-height: 1.7;
}
.faq-item.open .faq-answer { max-height: 200px; padding: 16px 20px; }

/* ===== Toast Notifications ===== */
.toast-container {
  position: fixed; bottom: 24px; right: 24px;
  z-index: 9999; display: flex; flex-direction: column; gap: 8px;
}
.toast {
  display: flex; align-items: center; gap: 12px;
  padding: 14px 18px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  font-size: 0.875rem;
  min-width: 280px;
  animation: slideInRight 0.3s ease;
  border-left: 3px solid var(--accent);
}
.toast.success { border-left-color: var(--success); }
.toast.error { border-left-color: var(--error); }

/* ===== Sidebar ===== */
.sidebar {
  width: var(--sidebar-w);
  position: fixed; top: var(--navbar-h); left: 0; bottom: 0;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border-subtle);
  overflow-y: auto; padding: 20px 12px;
  z-index: 100;
}
.sidebar-section { margin-bottom: 24px; }
.sidebar-label {
  font-size: 0.7rem; font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase; letter-spacing: 0.8px;
  padding: 0 8px;
  margin-bottom: 6px;
}
.sidebar-link {
  display: flex; align-items: center; gap: 10px;
  padding: 8px 12px;
  border-radius: var(--radius-sm);
  font-size: 0.875rem; font-weight: 500;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
  margin-bottom: 2px;
}
.sidebar-link:hover { background: rgba(249,115,22,0.08); color: var(--text-primary); }
.sidebar-link.active { background: rgba(249,115,22,0.12); color: var(--accent); }
.sidebar-link .link-icon { font-size: 1rem; opacity: 0.8; }

/* ===== Table ===== */
.table-container {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow: hidden;
}
table { width: 100%; border-collapse: collapse; }
thead { background: var(--bg-elevated); }
th {
  padding: 12px 16px;
  font-size: 0.78rem; font-weight: 700;
  color: var(--text-muted);
  text-align: left; text-transform: uppercase; letter-spacing: 0.5px;
  border-bottom: 1px solid var(--border-subtle);
}
td {
  padding: 14px 16px;
  font-size: 0.875rem;
  color: var(--text-primary);
  border-bottom: 1px solid var(--border-subtle);
}
tr:last-child td { border-bottom: none; }
tbody tr:hover { background: var(--bg-card-hover); }

/* ===== Quiz ===== */
.quiz-option {
  display: flex; align-items: center; gap: 12px;
  padding: 14px 18px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: 0.9rem;
}
.quiz-option:hover { border-color: var(--border-color); background: var(--bg-card-hover); }
.quiz-option.selected { border-color: var(--accent); background: rgba(249,115,22,0.1); }
.quiz-option.correct { border-color: var(--success); background: rgba(34,197,94,0.1); }
.quiz-option.wrong { border-color: var(--error); background: rgba(239,68,68,0.1); }
.option-letter {
  width: 28px; height: 28px;
  background: var(--bg-card);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-size: 0.8rem; font-weight: 700;
  color: var(--text-muted);
  flex-shrink: 0;
}
.quiz-option.selected .option-letter { background: var(--accent); color: #fff; }

/* ===== Footer ===== */
footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  padding: 48px 0 24px;
}
.footer-grid { display: grid; grid-template-columns: 2fr 1fr 1fr 1fr; gap: 40px; margin-bottom: 40px; }
.footer-brand-desc { font-size: 0.875rem; color: var(--text-muted); margin-top: 10px; line-height: 1.6; }
.footer-col-title { font-size: 0.82rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.5px; color: var(--text-muted); margin-bottom: 14px; }
.footer-links { display: flex; flex-direction: column; gap: 8px; }
.footer-links a { font-size: 0.875rem; color: var(--text-muted); transition: color var(--transition-fast); }
.footer-links a:hover { color: var(--accent); }
.footer-bottom { display: flex; align-items: center; justify-content: space-between; padding-top: 24px; border-top: 1px solid var(--border-subtle); }
.footer-copy { font-size: 0.8rem; color: var(--text-muted); }

/* ===== Animations ===== */
@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-16px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}
@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-12px); }
}
@keyframes pulse-glow {
  0%, 100% { box-shadow: 0 0 16px rgba(249,115,22,0.2); }
  50% { box-shadow: 0 0 32px rgba(249,115,22,0.5); }
}
@keyframes slideInRight {
  from { opacity: 0; transform: translateX(24px); }
  to { opacity: 1; transform: translateX(0); }
}
@keyframes spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}
@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0; }
}
@keyframes barGrow {
  from { height: 0; }
  to { height: var(--target-h); }
}

.animate-fade-in { animation: fadeIn 0.5s ease; }
.animate-float { animation: float 3s ease-in-out infinite; }
.animate-pulse-glow { animation: pulse-glow 2s ease-in-out infinite; }

/* Typing cursor */
.typing-cursor::after {
  content: '|';
  animation: blink 1s step-end infinite;
  color: var(--accent);
}

/* ===== Grid Systems ===== */
.grid-2 { display: grid; grid-template-columns: repeat(2, 1fr); gap: 20px; }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.grid-4 { display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px; }
.algo-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 20px; }

/* ===== Layout Utilities ===== */
.page-wrapper { padding-top: var(--navbar-h); min-height: 100vh; }
.with-sidebar { padding-left: var(--sidebar-w); }
.content-area { padding: 32px; max-width: 100%; }
.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-between { justify-content: space-between; }
.gap-2 { gap: 8px; }
.gap-3 { gap: 12px; }
.gap-4 { gap: 16px; }
.gap-6 { gap: 24px; }
.mt-2 { margin-top: 8px; }
.mt-4 { margin-top: 16px; }
.mt-6 { margin-top: 24px; }
.mb-2 { margin-bottom: 8px; }
.mb-4 { margin-bottom: 16px; }
.mb-6 { margin-bottom: 24px; }
.w-full { width: 100%; }
.text-center { text-align: center; }
.text-muted { color: var(--text-muted); }
.text-accent { color: var(--accent); }
.font-mono { font-family: var(--font-mono); }
.truncate { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

/* Divider */
.divider { height: 1px; background: var(--border-subtle); margin: 24px 0; }

/* Algorithm page main layout */
.algo-main-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin-bottom: 20px;
}
@media (max-width: 768px) {
  .algo-main-layout { grid-template-columns: 1fr; }
}

/* Compare page controls grid */
.compare-controls {
  display: grid;
  grid-template-columns: 1fr 1fr auto;
  gap: 16px;
  align-items: end;
}
@media (max-width: 768px) {
  .compare-controls { grid-template-columns: 1fr; }
}

/* ===== Responsive Design ===== */

/* Prevent horizontal overflow globally */
html { overflow-x: hidden; }

@media (max-width: 1024px) {
  .sidebar { display: none; }
  .with-sidebar { padding-left: 0; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 28px; }

  /* Admin sidebar collapse */
  .admin-sidebar { display: none; }
  .admin-content { margin-left: 0; }
}

@media (max-width: 768px) {
  .navbar-links { display: none; }
  .nav-toggle { display: flex; }
  .bottom-nav { display: flex; }
  .page-wrapper { padding-bottom: 70px; }
  .section { padding: 60px 0; }
  .container { padding: 0 16px; }
  .hero { min-height: calc(100vh - 64px); align-items: flex-start; padding-top: calc(var(--navbar-h) + 40px); }
  .hero-title { font-size: clamp(2rem, 8vw, 3rem); }
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; gap: 20px; }
  .footer-bottom { flex-direction: column; gap: 12px; text-align: center; }
  .hero-stats { gap: 20px; }
  .viz-controls { justify-content: center; flex-wrap: wrap; }
  .speed-control { margin-left: 0; width: 100%; justify-content: center; }
  .algo-grid { grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); gap: 14px; }

  /* Content area reduced padding */
  .content-area { padding: 16px; }

  /* Code panel header — wrap language buttons */
  .code-header { flex-wrap: wrap; gap: 8px; padding: 10px 12px; }

  /* Code body — reduce padding, prevent overflow */
  .code-body { padding: 12px; }
  .code-body pre { font-size: 0.75rem; white-space: pre-wrap; word-break: break-word; }

  /* Tabs — horizontal scroll mode on mobile */
  .tabs {
    overflow-x: auto;
    flex-wrap: nowrap;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
  }
  .tabs::-webkit-scrollbar { display: none; }
  .tab-btn { flex-shrink: 0; white-space: nowrap; }

  /* Table scroll container */
  .table-container { overflow-x: auto; -webkit-overflow-scrolling: touch; }

  /* Visualization container constrain */
  .viz-container { max-width: 100%; }

  /* Hero floating cards — hide on mobile to prevent overflow */
  .floating-card { display: none; }

  /* Hero visual — hide on mobile */
  .hero-visual { display: none !important; }

  /* Hero container — force single column */
  .hero > .container { display: flex !important; flex-direction: column !important; }

  /* Navbar — prevent overflow */
  .navbar {
    overflow: hidden;
    gap: 8px;
  }
  .navbar-actions {
    gap: 6px;
    flex-shrink: 0;
  }

  /* Hide user area on mobile (users access profile via bottom nav) */
  #navUserArea { display: none !important; }

  /* Bottom nav — ensure all 5 items fit */
  .bottom-nav {
    padding: 6px 0;
    gap: 0;
  }
  .bottom-nav-item {
    padding: 4px 8px;
    font-size: 0.6rem;
    min-width: 0;
  }
  .bottom-nav-item .nav-icon { font-size: 1.1rem; }

  /* Navbar brand text size */
  .navbar-brand { font-size: 1rem; }

  /* Toast narrower */
  .toast { min-width: auto; max-width: calc(100vw - 48px); }
  .toast-container { right: 12px; left: 12px; bottom: 80px; }

  /* Card padding reduce on mobile */
  .card { padding: 16px; }

  /* FAQ answer */
  .faq-item.open .faq-answer { max-height: 300px; }

  /* Step panel */
  .step-panel { padding: 14px; }

  /* Stat cards */
  .stat-card { padding: 14px; }
  .stat-value { font-size: 1.5rem; }
}

@media (max-width: 480px) {
  .hero-actions { flex-direction: column; width: 100%; }
  .hero-actions .btn { width: 100%; justify-content: center; }
  .algo-grid { grid-template-columns: 1fr; }
  .grid-4 { grid-template-columns: 1fr 1fr; }

  /* Even smaller code font */
  .code-body pre { font-size: 0.7rem; }

  /* Reduce section padding */
  .section { padding: 40px 0; }
  .container { padding: 0 12px; }
  .content-area { padding: 12px; }

  /* Reduce hero stats size */
  .hero-stat-val { font-size: 1.4rem; }
  .hero-stats { gap: 16px; }

  /* Section header tighter */
  .section-header { margin-bottom: 32px; }
  .section-title { font-size: clamp(1.4rem, 5vw, 2rem); }

  /* Navbar padding */
  .navbar { padding: 0 12px; }
}

/* ===== Tooltip ===== */
.tooltip { position: relative; }
.tooltip::after {
  content: attr(data-tip);
  position: absolute; bottom: calc(100% + 6px); left: 50%; transform: translateX(-50%);
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  color: var(--text-primary);
  font-size: 0.75rem;
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  white-space: nowrap;
  pointer-events: none;
  opacity: 0;
  transition: opacity var(--transition-fast);
}
.tooltip:hover::after { opacity: 1; }

/* ===== Admin Specific ===== */
.admin-sidebar {
  width: 240px;
  position: fixed; top: 0; left: 0; bottom: 0;
  background: #0d0d14;
  border-right: 1px solid rgba(255,255,255,0.06);
  padding: 24px 12px;
  z-index: 100;
  overflow-y: auto;
}
.admin-content {
  margin-left: 240px;
  padding: 24px;
  min-height: 100vh;
  background: var(--bg-primary);
}
.admin-stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 20px;
  display: flex; gap: 16px; align-items: flex-start;
}
.admin-stat-icon {
  width: 44px; height: 44px;
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.2rem;
  flex-shrink: 0;
}
.admin-stat-val { font-size: 1.8rem; font-weight: 800; }
.admin-stat-label { font-size: 0.8rem; color: var(--text-muted); }

/* Algo bar chart visualization */
.bar-viz {
  display: flex;
  align-items: flex-end;
  justify-content: center;
  gap: 3px;
  width: 100%;
  height: 100%;
  padding: 12px;
}
.bar {
  flex: 1; max-width: 40px;
  border-radius: 4px 4px 0 0;
  transition: all 0.15s ease;
  position: relative;
  min-width: 12px;
}

/* Learning path */
.path-node {
  display: flex; align-items: center; gap: 12px;
  padding: 14px 18px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
}
.path-node:hover { border-color: var(--border-color); }
.path-node.completed { border-color: rgba(34,197,94,0.3); }
.path-node.active { border-color: rgba(249,115,22,0.4); box-shadow: 0 0 16px rgba(249,115,22,0.1); }
.path-icon {
  width: 36px; height: 36px;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-size: 0.85rem; font-weight: 700;
  flex-shrink: 0;
}