/* ═══════════════════════════════════════════════════════════════
   DESIGN TOKENS — GLASSMORPHISM SYSTEM
═══════════════════════════════════════════════════════════════ */
:root {
  --font-display: 'Plus Jakarta Sans', system-ui, sans-serif;
  --font-body: 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  /* Accent palette */
  --accent: #7C3AED;
  --accent-light: #A78BFA;
  --accent-glow: rgba(124,58,237,0.35);
  --gold: #F59E0B;
  --gold-light: #FCD34D;
  --green: #10B981;
  --green-light: #34D399;
  --red: #EF4444;
  --red-light: #F87171;
  --blue: #3B82F6;
  --blue-light: #93C5FD;

  /* Category colors */
  --cat-algebra: #8B5CF6;
  --cat-geometry: #10B981;
  --cat-trigonometry: #F59E0B;
  --cat-calculus: #EF4444;
  --cat-statistics: #3B82F6;
  --cat-physics: #EC4899;
  --cat-number: #06B6D4;

  /* Easing */
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-in-out: cubic-bezier(0.4, 0, 0.2, 1);
}

/* DARK THEME (default) */
[data-theme="dark"] {
  --bg-base: #06060F;
  --bg-surface: #0D0D1A;
  --bg-elevated: #13132A;
  --glass-bg: rgba(255,255,255,0.04);
  --glass-bg-hover: rgba(255,255,255,0.07);
  --glass-border: rgba(255,255,255,0.10);
  --glass-border-hover: rgba(255,255,255,0.18);
  --glass-blur: blur(20px);
  --glass-shadow: 0 8px 32px rgba(0,0,0,0.5), inset 0 1px 0 rgba(255,255,255,0.06);
  --glass-shadow-hover: 0 20px 60px rgba(0,0,0,0.6), inset 0 1px 0 rgba(255,255,255,0.10);
  --text-primary: #F1F5F9;
  --text-secondary: #94A3B8;
  --text-dim: #475569;
  --text-accent: #A78BFA;
  --nav-bg: rgba(6,6,15,0.85);
  --modal-overlay: rgba(0,0,0,0.85);
  --skeleton-from: rgba(255,255,255,0.03);
  --skeleton-to: rgba(255,255,255,0.08);
  --scrollbar-track: rgba(255,255,255,0.03);
  --scrollbar-thumb: rgba(255,255,255,0.12);
}

/* LIGHT THEME */
[data-theme="light"] {
  --bg-base: #EEF0F8;
  --bg-surface: #F4F5FF;
  --bg-elevated: #FFFFFF;
  --glass-bg: rgba(255,255,255,0.55);
  --glass-bg-hover: rgba(255,255,255,0.75);
  --glass-border: rgba(120,100,200,0.15);
  --glass-border-hover: rgba(124,58,237,0.30);
  --glass-blur: blur(20px);
  --glass-shadow: 0 4px 24px rgba(100,80,200,0.10), inset 0 1px 0 rgba(255,255,255,0.8);
  --glass-shadow-hover: 0 12px 40px rgba(100,80,200,0.18), inset 0 1px 0 rgba(255,255,255,0.9);
  --text-primary: #0F172A;
  --text-secondary: #475569;
  --text-dim: #94A3B8;
  --text-accent: #7C3AED;
  --nav-bg: rgba(238,240,248,0.88);
  --modal-overlay: rgba(15,23,42,0.6);
  --skeleton-from: rgba(0,0,0,0.04);
  --skeleton-to: rgba(0,0,0,0.09);
  --scrollbar-track: rgba(0,0,0,0.04);
  --scrollbar-thumb: rgba(0,0,0,0.15);
}

/* ═══════════════════════════════════════════════════════════════
   RESET & BASE
═══════════════════════════════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

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

body {
  font-family: var(--font-body);
  background: var(--bg-base);
  color: var(--text-primary);
  min-height: 100vh;
  min-height: 100dvh;
  overflow-x: hidden;
  transition: background 0.3s var(--ease-in-out), color 0.3s var(--ease-in-out);
  -webkit-font-smoothing: antialiased;
}

/* Ambient background orbs */
body::before, body::after {
  content: '';
  position: fixed;
  border-radius: 50%;
  filter: blur(80px);
  pointer-events: none;
  z-index: 0;
  transition: opacity 0.5s;
}
body::before {
  width: 500px; height: 500px;
  background: radial-gradient(circle, rgba(124,58,237,0.12) 0%, transparent 70%);
  top: -100px; left: -100px;
}
body::after {
  width: 400px; height: 400px;
  background: radial-gradient(circle, rgba(245,158,11,0.08) 0%, transparent 70%);
  bottom: 0; right: -100px;
}
[data-theme="light"] body::before { background: radial-gradient(circle, rgba(124,58,237,0.08) 0%, transparent 70%); }
[data-theme="light"] body::after { background: radial-gradient(circle, rgba(245,158,11,0.05) 0%, transparent 70%); }

::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: var(--scrollbar-track); }
::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 99px; }

/* Focus ring */
:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 4px; }

/* ═══════════════════════════════════════════════════════════════
   TYPOGRAPHY SCALE
═══════════════════════════════════════════════════════════════ */
.t-display { font-family: var(--font-display); font-size: clamp(2rem, 5vw, 3.5rem); font-weight: 800; letter-spacing: -0.03em; line-height: 1.1; }
.t-h1 { font-family: var(--font-display); font-size: clamp(1.5rem, 3vw, 2rem); font-weight: 700; letter-spacing: -0.02em; }
.t-h2 { font-family: var(--font-display); font-size: 1.25rem; font-weight: 700; letter-spacing: -0.01em; }
.t-h3 { font-family: var(--font-display); font-size: 1rem; font-weight: 600; }
.t-body { font-size: 0.9375rem; line-height: 1.65; }
.t-small { font-size: 0.8125rem; line-height: 1.5; }
.t-label { font-size: 0.6875rem; font-weight: 600; letter-spacing: 0.07em; text-transform: uppercase; }
.t-mono { font-family: var(--font-mono); }

/* ═══════════════════════════════════════════════════════════════
   GLASS COMPONENTS
═══════════════════════════════════════════════════════════════ */
.glass {
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  box-shadow: var(--glass-shadow);
  border-radius: 20px;
  transition: background 0.25s, border-color 0.25s, box-shadow 0.25s, transform 0.25s var(--ease-spring);
}
.glass:hover {
  background: var(--glass-bg-hover);
  border-color: var(--glass-border-hover);
  box-shadow: var(--glass-shadow-hover);
}
.glass-flat {
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
}

/* ═══════════════════════════════════════════════════════════════
   TOP NAVIGATION (Desktop ≥ 768px)
═══════════════════════════════════════════════════════════════ */
#top-nav {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0;
  height: 64px;
  z-index: 900;
  background: var(--nav-bg);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border-bottom: 1px solid var(--glass-border);
  padding: 0 32px;
  align-items: center;
  gap: 32px;
  transition: background 0.3s;
}
.nav-logo {
  display: flex; align-items: center; gap: 10px;
  text-decoration: none; flex-shrink: 0;
}
.nav-logo-icon {
  width: 36px; height: 36px;
  background: linear-gradient(135deg, var(--accent), var(--gold));
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  font-size: 18px; font-weight: 800; color: white;
  font-family: var(--font-mono);
  box-shadow: 0 4px 12px var(--accent-glow);
}
.nav-logo-text { font-family: var(--font-display); font-weight: 800; font-size: 1.1rem; color: var(--text-primary); }
.nav-logo-sub { font-size: 0.65rem; color: var(--text-secondary); letter-spacing: 0.05em; }
.nav-links { display: flex; gap: 4px; }
.nav-link {
  padding: 8px 16px; border-radius: 10px;
  font-size: 0.875rem; font-weight: 500; color: var(--text-secondary);
  text-decoration: none; cursor: pointer; border: none; background: none;
  transition: all 0.2s; font-family: var(--font-body);
}
.nav-link:hover, .nav-link.active { color: var(--text-primary); background: var(--glass-bg-hover); }
.nav-link.active { color: var(--accent-light); }
.nav-spacer { flex: 1; }
.nav-search-bar {
  flex: 0 1 340px;
  display: flex; align-items: center; gap: 8px;
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 12px;
  padding: 0 14px;
  height: 40px;
  transition: border-color 0.2s, box-shadow 0.2s;
}
.nav-search-bar:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}
.nav-search-bar input {
  flex: 1; background: none; border: none; outline: none;
  font-family: var(--font-body); font-size: 0.875rem;
  color: var(--text-primary);
}
.nav-search-bar input::placeholder { color: var(--text-dim); }
.search-icon { color: var(--text-dim); font-size: 14px; }
.nav-actions { display: flex; align-items: center; gap: 8px; }
.nav-btn {
  width: 38px; height: 38px; border-radius: 10px;
  border: 1px solid var(--glass-border);
  background: var(--glass-bg);
  color: var(--text-secondary);
  cursor: pointer; font-size: 16px;
  display: flex; align-items: center; justify-content: center;
  transition: all 0.2s;
}
.nav-btn:hover { background: var(--glass-bg-hover); color: var(--text-primary); border-color: var(--glass-border-hover); }

/* ═══════════════════════════════════════════════════════════════
   BOTTOM NAVIGATION (Mobile < 768px)
═══════════════════════════════════════════════════════════════ */
#bottom-nav {
  position: fixed;
  bottom: 0; left: 0; right: 0;
  z-index: 900;
  background: var(--nav-bg);
  backdrop-filter: blur(24px);
  -webkit-backdrop-filter: blur(24px);
  border-top: 1px solid var(--glass-border);
  display: flex;
  padding-bottom: env(safe-area-inset-bottom);
  transition: background 0.3s;
}
.bottom-nav-item {
  flex: 1; display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  padding: 10px 4px 8px;
  cursor: pointer; border: none; background: none;
  transition: all 0.2s;
  position: relative;
  color: var(--text-dim);
  font-family: var(--font-body);
  -webkit-tap-highlight-color: transparent;
}
.bottom-nav-item.active { color: var(--accent-light); }
.bottom-nav-item.active .bnav-icon { transform: translateY(-2px); }
.bottom-nav-item::after {
  content: '';
  position: absolute;
  top: 0; left: 50%; transform: translateX(-50%);
  width: 0; height: 2px;
  background: var(--accent);
  border-radius: 0 0 4px 4px;
  transition: width 0.3s var(--ease-spring);
}
.bottom-nav-item.active::after { width: 24px; }
.bnav-icon { font-size: 22px; line-height: 1; transition: transform 0.2s var(--ease-spring); }
.bnav-label { font-size: 0.625rem; font-weight: 600; letter-spacing: 0.04em; margin-top: 3px; }

/* ═══════════════════════════════════════════════════════════════
   MOBILE SEARCH BAR
═══════════════════════════════════════════════════════════════ */
#mobile-search {
  display: flex;
  align-items: center; gap: 10px;
  margin: 12px 16px;
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 14px;
  padding: 0 16px;
  height: 46px;
  backdrop-filter: var(--glass-blur);
  transition: border-color 0.2s, box-shadow 0.2s;
}
#mobile-search:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}
#mobile-search input {
  flex: 1; background: none; border: none; outline: none;
  font-family: var(--font-body); font-size: 0.9375rem;
  color: var(--text-primary);
}
#mobile-search input::placeholder { color: var(--text-dim); }

/* ═══════════════════════════════════════════════════════════════
   LAYOUT / PAGES
═══════════════════════════════════════════════════════════════ */
#app {
  position: relative; z-index: 1;
  min-height: 100dvh;
  padding-top: 0;
  padding-bottom: calc(72px + env(safe-area-inset-bottom));
}
.page { display: none; }
.page.active { display: block; }

/* ═══════════════════════════════════════════════════════════════
   HOME PAGE — HERO
═══════════════════════════════════════════════════════════════ */
#hero {
  padding: 48px 20px 32px;
  text-align: center;
  position: relative;
}
.hero-badge {
  display: inline-flex; align-items: center; gap: 6px;
  background: rgba(124,58,237,0.15);
  border: 1px solid rgba(124,58,237,0.3);
  border-radius: 99px;
  padding: 5px 14px;
  font-size: 0.75rem; font-weight: 600;
  color: var(--accent-light);
  margin-bottom: 20px;
  letter-spacing: 0.04em;
}
.hero-title {
  font-family: var(--font-display);
  font-size: clamp(2rem, 8vw, 3.2rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin-bottom: 14px;
}
.hero-title .grad {
  background: linear-gradient(135deg, var(--accent-light), var(--gold));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-sub {
  font-size: 1rem; color: var(--text-secondary);
  max-width: 500px; margin: 0 auto 28px;
  line-height: 1.6;
}
.hero-stats {
  display: flex; justify-content: center; gap: 32px;
  flex-wrap: wrap;
}
.stat-item { text-align: center; }
.stat-num {
  font-family: var(--font-display);
  font-size: 1.5rem; font-weight: 800;
  color: var(--text-primary);
}
.stat-num span { color: var(--accent-light); }
.stat-label { font-size: 0.75rem; color: var(--text-secondary); }

/* ═══════════════════════════════════════════════════════════════
   FILTERS — CATEGORY & GRADE
═══════════════════════════════════════════════════════════════ */
.filters-section { padding: 0 16px 16px; }
.filter-group-label {
  font-size: 0.6875rem; font-weight: 600;
  color: var(--text-dim); letter-spacing: 0.07em;
  text-transform: uppercase;
  margin-bottom: 8px; margin-top: 14px;
}
.filter-scroll {
  display: flex; gap: 8px;
  overflow-x: auto; padding-bottom: 4px;
  -ms-overflow-style: none; scrollbar-width: none;
}
.filter-scroll::-webkit-scrollbar { display: none; }
.filter-chip {
  flex-shrink: 0;
  padding: 7px 14px; border-radius: 99px;
  font-size: 0.8125rem; font-weight: 600;
  cursor: pointer; border: 1px solid var(--glass-border);
  background: var(--glass-bg);
  color: var(--text-secondary);
  backdrop-filter: var(--glass-blur);
  transition: all 0.2s;
  white-space: nowrap;
  font-family: var(--font-body);
  -webkit-tap-highlight-color: transparent;
}
.filter-chip:hover { border-color: var(--glass-border-hover); color: var(--text-primary); }
.filter-chip.active {
  background: var(--accent);
  border-color: var(--accent);
  color: white;
  box-shadow: 0 4px 14px var(--accent-glow);
}
.filter-chip[data-cat="Algebra"].active { background: var(--cat-algebra); border-color: var(--cat-algebra); box-shadow: 0 4px 14px rgba(139,92,246,0.4); }
.filter-chip[data-cat="Geometry"].active { background: var(--cat-geometry); border-color: var(--cat-geometry); box-shadow: 0 4px 14px rgba(16,185,129,0.4); }
.filter-chip[data-cat="Trigonometry"].active { background: var(--cat-trigonometry); border-color: var(--cat-trigonometry); box-shadow: 0 4px 14px rgba(245,158,11,0.4); }
.filter-chip[data-cat="Calculus"].active { background: var(--cat-calculus); border-color: var(--cat-calculus); box-shadow: 0 4px 14px rgba(239,68,68,0.4); }
.filter-chip[data-cat="Statistics"].active { background: var(--cat-statistics); border-color: var(--cat-statistics); box-shadow: 0 4px 14px rgba(59,130,246,0.4); }
.filter-chip[data-cat="Physics"].active { background: var(--cat-physics); border-color: var(--cat-physics); box-shadow: 0 4px 14px rgba(236,72,153,0.4); }

/* ═══════════════════════════════════════════════════════════════
   FORMULA GRID
═══════════════════════════════════════════════════════════════ */
#formula-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
  padding: 8px 16px 16px;
}
.formula-card {
  position: relative; overflow: hidden;
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  box-shadow: var(--glass-shadow);
  border-radius: 20px;
  padding: 20px;
  cursor: pointer;
  transition: transform 0.25s var(--ease-spring), box-shadow 0.25s, border-color 0.25s, background 0.25s;
  animation: cardEntrance 0.4s var(--ease-out) both;
  -webkit-tap-highlight-color: transparent;
}
.formula-card:hover {
  transform: translateY(-5px);
  background: var(--glass-bg-hover);
  border-color: var(--glass-border-hover);
}
.formula-card:active { transform: scale(0.97); }

.card-top-bar {
  position: absolute; top: 0; left: 0; right: 0;
  height: 3px; border-radius: 20px 20px 0 0;
}
.card-header { display: flex; align-items: flex-start; justify-content: space-between; margin-bottom: 12px; }
.card-badges { display: flex; gap: 6px; flex-wrap: wrap; }
.badge {
  padding: 3px 9px; border-radius: 99px;
  font-size: 0.6875rem; font-weight: 700;
  letter-spacing: 0.04em;
}
.badge-cat { color: white; }
.badge-grade { background: var(--glass-bg); border: 1px solid var(--glass-border); color: var(--text-secondary); }
.badge-diff-easy { background: rgba(16,185,129,0.15); color: var(--green); border: 1px solid rgba(16,185,129,0.2); }
.badge-diff-medium { background: rgba(245,158,11,0.15); color: var(--gold); border: 1px solid rgba(245,158,11,0.2); }
.badge-diff-hard { background: rgba(239,68,68,0.15); color: var(--red); border: 1px solid rgba(239,68,68,0.2); }
.badge-diff-advanced { background: rgba(124,58,237,0.15); color: var(--accent-light); border: 1px solid rgba(124,58,237,0.2); }

.card-name { font-family: var(--font-display); font-size: 1rem; font-weight: 700; margin-bottom: 6px; line-height: 1.3; }
.card-formula {
  font-family: var(--font-mono); font-size: 0.875rem;
  margin-bottom: 10px; line-height: 1.4;
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.card-tagline { font-size: 0.8125rem; color: var(--text-secondary); line-height: 1.4; margin-bottom: 14px; }
.card-footer { display: flex; align-items: center; justify-content: space-between; }
.card-chips { display: flex; gap: 5px; }
.card-chip {
  font-size: 0.625rem; font-weight: 600; letter-spacing: 0.04em;
  padding: 3px 8px; border-radius: 6px;
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  color: var(--text-dim);
}
.card-arrow { color: var(--text-dim); font-size: 14px; transition: transform 0.2s; }
.formula-card:hover .card-arrow { transform: translateX(3px); }

/* Category color helpers */
.cat-Algebra   { --cat: var(--cat-algebra);   }
.cat-Geometry  { --cat: var(--cat-geometry);  }
.cat-Trigonometry { --cat: var(--cat-trigonometry); }
.cat-Calculus  { --cat: var(--cat-calculus);  }
.cat-Statistics{ --cat: var(--cat-statistics);}
.cat-Physics   { --cat: var(--cat-physics);   }
.cat-Number    { --cat: var(--cat-number);    }

.card-top-bar  { background: var(--cat); }
.badge-cat     { background: var(--cat); }
.card-formula  { color: var(--cat); }
.formula-card:hover { box-shadow: 0 20px 60px rgba(0,0,0,0.4), 0 0 0 1px var(--cat), inset 0 1px 0 rgba(255,255,255,0.08); border-color: var(--cat); }

/* Empty state */
.empty-state {
  grid-column: 1 / -1;
  text-align: center; padding: 80px 20px;
  color: var(--text-dim);
}
.empty-icon { font-size: 48px; margin-bottom: 16px; opacity: 0.5; }
.empty-text { font-size: 1.1rem; font-weight: 600; color: var(--text-secondary); margin-bottom: 8px; }
.empty-sub { font-size: 0.875rem; }

/* ═══════════════════════════════════════════════════════════════
   SEARCH RESULTS
═══════════════════════════════════════════════════════════════ */
#search-results-banner {
  display: none;
  padding: 12px 16px;
  font-size: 0.875rem;
  color: var(--text-secondary);
}
#search-results-banner b { color: var(--accent-light); }

/* ═══════════════════════════════════════════════════════════════
   MODAL — FORMULA DETAIL
═══════════════════════════════════════════════════════════════ */
#modal-overlay {
  position: fixed; inset: 0;
  background: var(--modal-overlay);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 1000;
  display: none; align-items: flex-end; justify-content: center;
  padding: 0;
  transition: opacity 0.3s;
}
#modal-overlay.open { display: flex; }

@media (min-width: 640px) {
  #modal-overlay { align-items: center; padding: 16px; }
}

#modal {
  background: var(--bg-surface);
  border: 1px solid var(--glass-border);
  border-radius: 28px 28px 0 0;
  width: 100%; max-width: 680px;
  max-height: 92dvh;
  overflow: hidden;
  display: flex; flex-direction: column;
  animation: modalSlideUp 0.35s var(--ease-spring);
  position: relative;
  transition: max-width 0.3s, max-height 0.3s, border-radius 0.3s;
}
@media (min-width: 640px) {
  #modal { border-radius: 28px; max-height: 90vh; max-width: 720px; }
}
@media (min-width: 1024px) {
  #modal { max-width: 900px; max-height: 88vh; }
}
@media (min-width: 1400px) {
  #modal { max-width: 1080px; }
}
#modal.fullscreen {
  max-width: 100vw !important; max-height: 100dvh !important;
  border-radius: 0 !important; margin: 0;
}
/* Fullscreen toggle button */
.modal-fullscreen-btn {
  position: absolute; top: 14px; right: 14px;
  background: rgba(255,255,255,0.06); border: 1px solid var(--glass-border);
  color: var(--text-secondary); border-radius: 8px;
  width: 30px; height: 30px; cursor: pointer; font-size: 0.875rem;
  display: flex; align-items: center; justify-content: center;
  z-index: 10; transition: background 0.15s;
}
.modal-fullscreen-btn:hover { background: rgba(255,255,255,0.12); }

.modal-drag-handle {
  width: 36px; height: 4px;
  background: var(--glass-border);
  border-radius: 99px;
  margin: 12px auto 0;
  flex-shrink: 0;
}
@media (min-width: 640px) { .modal-drag-handle { display: none; } }

.modal-header {
  padding: 16px 20px 0;
  flex-shrink: 0;
  position: sticky; top: 0;
  background: var(--bg-surface);
  z-index: 10;
  border-bottom: 1px solid var(--glass-border);
  padding-bottom: 0;
}
.modal-header-top { display: flex; align-items: flex-start; gap: 12px; margin-bottom: 14px; }
.modal-header-info { flex: 1; }
.modal-badges { display: flex; gap: 6px; margin-bottom: 8px; flex-wrap: wrap; }
.modal-name { font-family: var(--font-display); font-size: 1.2rem; font-weight: 800; line-height: 1.2; margin-bottom: 4px; }
.modal-formula-display {
  font-family: var(--font-mono); font-size: 1rem; font-weight: 600;
  margin-bottom: 4px;
  overflow-x: auto;
}
.modal-tagline { font-size: 0.8125rem; color: var(--text-secondary); }

.modal-close {
  width: 36px; height: 36px; border-radius: 10px;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  color: var(--text-secondary); cursor: pointer; font-size: 16px;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0; transition: all 0.2s; margin-top: 2px;
}
.modal-close:hover { background: var(--glass-bg-hover); color: var(--text-primary); }

/* Tabs */
.modal-tabs {
  display: flex; gap: 2px; overflow-x: auto;
  padding: 0 4px;
  -ms-overflow-style: none; scrollbar-width: none;
}
.modal-tabs::-webkit-scrollbar { display: none; }
.tab-btn {
  flex-shrink: 0;
  padding: 10px 16px; border: none; background: none;
  font-family: var(--font-body); font-size: 0.8125rem; font-weight: 600;
  color: var(--text-secondary); cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: all 0.2s;
  -webkit-tap-highlight-color: transparent;
}
.tab-btn:hover { color: var(--text-primary); }
.tab-btn.active { color: var(--accent-light); border-bottom-color: var(--accent); }

/* Modal content area */
.modal-body {
  flex: 1; overflow-y: auto;
  padding: 20px;
  -webkit-overflow-scrolling: touch;
}

/* Tab panels */
.tab-panel { display: none; animation: fadeSlideIn 0.25s var(--ease-out); }
.tab-panel.active { display: block; }

/* ═══════════════════════════════════════════════════════════════
   TAB 1 — VISUAL
═══════════════════════════════════════════════════════════════ */
.vis-canvas-wrap {
  --vis-h: clamp(280px, 42vw, 520px); /* default responsive height */

  position: relative;
  width: 100%;
  height: var(--vis-h);
  min-height: 280px;
  max-height: 70vh;

  border-radius: 16px;
  overflow: hidden;
  background: var(--bg-base);
  border: 1px solid var(--glass-border);
  margin-bottom: 16px;
  touch-action: none;
}

.vis-canvas-wrap.canvas-sm { --vis-h: clamp(260px, 34vw, 340px); }
.vis-canvas-wrap.canvas-md { --vis-h: clamp(300px, 42vw, 460px); }
.vis-canvas-wrap.canvas-lg { --vis-h: clamp(360px, 50vw, 580px); }
.vis-canvas-wrap.canvas-xl { --vis-h: clamp(420px, 58vw, 680px); }

.vis-canvas-wrap canvas {
  width: 100%;
  height: 100%;
  display: block;
}

.vis-toolbar {
  position: absolute;
  top: 10px;
  right: 10px;
  display: flex;
  gap: 6px;
  z-index: 4;
}

.vis-btn {
  width: 32px;
  height: 32px;
  border-radius: 8px;
  background: rgba(0,0,0,0.5);
  backdrop-filter: blur(8px);
  border: 1px solid rgba(255,255,255,0.15);
  color: rgba(255,255,255,0.8);
  font-size: 13px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s;
}

.vis-btn:hover { background: rgba(124,58,237,0.5); }
.vis-btn.active { background: var(--accent); }

/* optional: slightly smaller visual area on narrow screens */
@media (max-width: 640px) {
  .vis-canvas-wrap {
    --vis-h: clamp(260px, 58vw, 420px);
    min-height: 260px;
  }
}

/* ── PARAM SLIDERS / CONTROLS ───────────────────────────── */
.params-section { margin-bottom: 8px; }

.param-label-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 6px;
}

.param-name {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--text-secondary);
  font-family: var(--font-mono);
}

.param-value {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--text-primary);
  font-family: var(--font-mono);
}

.param-slider {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 4px;
  border-radius: 99px;
  background: var(--glass-border);
  outline: none;
  cursor: pointer;
  margin-bottom: 12px;
}

.param-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 2px 8px var(--accent-glow);
  cursor: pointer;
  transition: transform 0.15s;
}

.param-slider::-webkit-slider-thumb:hover {
  transform: scale(1.2);
}

.param-slider::-moz-range-thumb {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  border: none;
  cursor: pointer;
}

.param-range {
  display: flex;
  justify-content: space-between;
}

.param-range span {
  font-size: 0.625rem;
  color: var(--text-dim);
  font-family: var(--font-mono);
}
/* ═══════════════════════════════════════════════════════════════
   TAB 2 — EXPLAIN
═══════════════════════════════════════════════════════════════ */
.explain-section {
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 16px;
  padding: 16px;
  margin-bottom: 14px;
}
.explain-section-title {
  font-size: 0.6875rem; font-weight: 700;
  letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--text-dim); margin-bottom: 10px;
  display: flex; align-items: center; gap: 6px;
}
.explain-text { font-size: 0.9375rem; line-height: 1.7; color: var(--text-primary); }

.story-card {
  background: linear-gradient(135deg, rgba(245,158,11,0.08), rgba(245,158,11,0.03));
  border: 1px solid rgba(245,158,11,0.2);
  border-radius: 16px; padding: 16px; margin-bottom: 14px;
}
.story-icon { font-size: 24px; margin-bottom: 8px; }
.story-title { font-size: 0.6875rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--gold); margin-bottom: 8px; }
.story-text { font-size: 0.9375rem; line-height: 1.7; color: var(--text-primary); }

.variables-grid {
  display: grid; gap: 8px;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  margin-bottom: 14px;
}
.variable-card {
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 12px; padding: 12px;
}
.var-symbol {
  font-family: var(--font-mono); font-size: 1.2rem; font-weight: 700;
  color: var(--text-accent); margin-bottom: 4px;
}
.var-name { font-size: 0.8125rem; font-weight: 600; color: var(--text-primary); margin-bottom: 2px; }
.var-unit { font-size: 0.75rem; color: var(--text-secondary); font-family: var(--font-mono); }

/* TTS Controls */
.tts-bar {
  display: flex; align-items: center; gap: 10px;
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 14px; padding: 10px 14px;
  margin-bottom: 14px;
}
.tts-btn {
  width: 38px; height: 38px; border-radius: 10px;
  background: var(--accent); border: none;
  color: white; font-size: 16px; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0; transition: all 0.2s;
  box-shadow: 0 4px 12px var(--accent-glow);
}
.tts-btn:hover { transform: scale(1.05); }
.tts-btn.playing { background: var(--red); box-shadow: 0 4px 12px rgba(239,68,68,0.4); }
.tts-label { flex: 1; font-size: 0.8125rem; color: var(--text-secondary); }
.tts-speed { display: flex; gap: 4px; }
.speed-btn {
  padding: 4px 8px; border-radius: 6px;
  border: 1px solid var(--glass-border);
  background: var(--glass-bg);
  font-size: 0.6875rem; font-weight: 600;
  color: var(--text-secondary); cursor: pointer;
  transition: all 0.2s; font-family: var(--font-body);
}
.speed-btn.active { background: var(--accent); border-color: var(--accent); color: white; }

.mistakes-list li {
  font-size: 0.875rem; color: var(--text-secondary);
  line-height: 1.6; padding: 6px 0;
  padding-left: 20px; position: relative;
  list-style: none;
}
.mistakes-list li::before {
  content: '⚠'; position: absolute; left: 0;
  font-size: 12px; top: 7px;
}

/* ═══════════════════════════════════════════════════════════════
   TAB 3 — DERIVATION (renders via StepPlayer — see .step-player-* rules)
═══════════════════════════════════════════════════════════════ */
.deriv-intro { font-size: 0.875rem; color: var(--text-secondary); margin-bottom: 16px; line-height: 1.6; }
.deriv-steps { display: flex; flex-direction: column; gap: 10px; }

.deriv-showall-btn {
  display: block; width: 100%; margin-top: 14px; padding: 11px;
  border-radius: 12px; border: 1px solid var(--glass-border);
  background: var(--glass-bg); color: var(--text-secondary);
  font-family: var(--font-body); font-size: 0.8125rem; font-weight: 600;
  cursor: pointer; transition: all 0.2s;
}
.deriv-showall-btn:hover { background: var(--glass-bg-hover); color: var(--text-primary); border-color: rgba(124,58,237,0.35); }

.deriv-all-steps { display: flex; flex-direction: column; gap: 10px; margin-top: 14px; }
.deriv-allstep-item {
  display: flex; gap: 12px; align-items: flex-start;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  border-radius: 14px; padding: 14px;
}
.deriv-allstep-num {
  width: 26px; height: 26px; border-radius: 8px; flex-shrink: 0; margin-top: 1px;
  background: rgba(124,58,237,0.12); border: 1px solid rgba(124,58,237,0.35);
  color: var(--accent-light); font-weight: 700; font-size: 0.8125rem;
  display: flex; align-items: center; justify-content: center;
}
.deriv-allstep-body { flex: 1; min-width: 0; }
.deriv-allstep-label { font-size: 0.75rem; color: var(--text-dim); margin-bottom: 4px; }
.deriv-allstep-expr {
  font-family: var(--font-mono); font-size: 0.9375rem; font-weight: 600;
  color: var(--text-primary); margin-bottom: 4px; word-break: break-word;
}
.deriv-allstep-note { font-size: 0.8125rem; color: var(--text-secondary); font-style: italic; }

/* ═══════════════════════════════════════════════════════════════
   TAB 4 — QUIZ
═══════════════════════════════════════════════════════════════ */
.quiz-progress {
  display: flex; gap: 6px; margin-bottom: 16px;
}
.quiz-dot {
  height: 4px; flex: 1; border-radius: 99px;
  background: var(--glass-border);
  transition: background 0.3s;
}
.quiz-dot.done { background: var(--green); }
.quiz-dot.current { background: var(--accent); }

.quiz-card {
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 16px; padding: 20px;
  margin-bottom: 14px;
}
.quiz-q-label { font-size: 0.6875rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--text-dim); margin-bottom: 10px; }
.quiz-question { font-size: 1rem; font-weight: 600; line-height: 1.5; color: var(--text-primary); margin-bottom: 14px; }
.quiz-hint-area {
  background: rgba(245,158,11,0.08);
  border: 1px solid rgba(245,158,11,0.2);
  border-radius: 10px; padding: 12px;
  margin-bottom: 12px; display: none;
}
.quiz-hint-label { font-size: 0.6875rem; font-weight: 700; color: var(--gold); margin-bottom: 4px; }
.quiz-hint-text { font-size: 0.875rem; color: var(--text-secondary); }
.quiz-answer-area {
  background: rgba(16,185,129,0.08);
  border: 1px solid rgba(16,185,129,0.25);
  border-radius: 10px; padding: 14px;
  display: none;
}
.quiz-answer-label { font-size: 0.6875rem; font-weight: 700; color: var(--green); margin-bottom: 6px; }
.quiz-answer-text { font-size: 0.9375rem; color: var(--text-primary); line-height: 1.6; }

.quiz-actions { display: flex; gap: 8px; flex-wrap: wrap; }
.quiz-btn {
  padding: 11px 20px; border-radius: 12px;
  font-family: var(--font-body); font-size: 0.875rem; font-weight: 600;
  cursor: pointer; transition: all 0.2s; border: 1px solid;
}
.quiz-btn-hint { background: rgba(245,158,11,0.1); border-color: rgba(245,158,11,0.25); color: var(--gold); }
.quiz-btn-hint:hover { background: rgba(245,158,11,0.2); }
.quiz-btn-reveal { background: var(--accent); border-color: var(--accent); color: white; box-shadow: 0 4px 14px var(--accent-glow); }
.quiz-btn-reveal:hover { transform: translateY(-1px); }
.quiz-btn-next { background: var(--green); border-color: var(--green); color: white; box-shadow: 0 4px 14px rgba(16,185,129,0.35); }
.quiz-btn-next:hover { transform: translateY(-1px); }

.quiz-complete {
  text-align: center; padding: 40px 20px;
}
.quiz-complete-icon { font-size: 48px; margin-bottom: 12px; }
.quiz-complete-title { font-family: var(--font-display); font-size: 1.3rem; font-weight: 800; margin-bottom: 8px; }
.quiz-complete-sub { color: var(--text-secondary); font-size: 0.9375rem; }

/* ═══════════════════════════════════════════════════════════════
   TAB 5 — VIDEOS
═══════════════════════════════════════════════════════════════ */
.video-item { margin-bottom: 16px; }
.video-embed { position: relative; padding-top: 56.25%; border-radius: 14px; overflow: hidden; background: #000; }
.video-embed iframe { position: absolute; inset: 0; width: 100%; height: 100%; border: none; }
.video-meta { padding: 10px 4px; }
.video-title { font-size: 0.9rem; font-weight: 600; color: var(--text-primary); margin-bottom: 3px; }
.video-channel { font-size: 0.8rem; color: var(--text-secondary); }
.video-linkout {
  display: flex; align-items: center; gap: 12px;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  border-radius: 14px; padding: 14px; text-decoration: none;
  transition: border-color 0.2s, background 0.2s;
}
.video-linkout:hover { border-color: rgba(124,58,237,0.4); background: rgba(124,58,237,0.06); }
.video-linkout-icon {
  width: 40px; height: 40px; border-radius: 10px; flex-shrink: 0;
  background: rgba(124,58,237,0.12); color: var(--accent-light);
  display: flex; align-items: center; justify-content: center; font-size: 1.1rem;
}
.video-linkout .video-meta { flex: 1; padding: 0; }
.video-linkout-arrow { font-size: 0.8125rem; font-weight: 600; color: var(--accent-light); white-space: nowrap; }

.no-videos {
  text-align: center; padding: 60px 20px;
  color: var(--text-dim);
}

/* ═══════════════════════════════════════════════════════════════
   TRICKS & TIPS TAB
═══════════════════════════════════════════════════════════════ */
.trick-item {
  display: flex; gap: 12px; align-items: flex-start;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  border-radius: 14px; padding: 14px; margin-bottom: 12px;
}
.trick-num {
  width: 26px; height: 26px; border-radius: 50%; flex-shrink: 0; margin-top: 1px;
  background: rgba(245,158,11,0.15); border: 1px solid rgba(245,158,11,0.4);
  color: var(--gold); font-weight: 700; font-size: 0.8125rem;
  display: flex; align-items: center; justify-content: center;
}
.trick-title { font-size: 0.9375rem; font-weight: 700; color: var(--text-primary); margin-bottom: 5px; }
.trick-text { font-size: 0.875rem; color: var(--text-secondary); line-height: 1.55; margin-bottom: 8px; }
.trick-example {
  font-size: 0.8125rem; color: var(--text-secondary);
  background: rgba(124,58,237,0.06); border: 1px solid rgba(124,58,237,0.2);
  border-radius: 10px; padding: 8px 10px; line-height: 1.5;
}
.trick-example-label {
  display: block; font-size: 0.6875rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: 0.05em; color: var(--accent-light); margin-bottom: 3px;
}

/* ═══════════════════════════════════════════════════════════════
   SOLVER PAGE
═══════════════════════════════════════════════════════════════ */
.solver-page { padding: 24px 16px; }
.solver-hero { text-align: center; margin-bottom: 28px; }
.solver-hero-icon { font-size: 48px; margin-bottom: 12px; }
.solver-hero-title { font-family: var(--font-display); font-size: 1.6rem; font-weight: 800; margin-bottom: 8px; }
.solver-hero-sub { color: var(--text-secondary); font-size: 0.9375rem; line-height: 1.6; }

.solver-input-card {
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  border-radius: 20px; padding: 20px;
  margin-bottom: 20px;
}
.solver-input-label { font-size: 0.8125rem; font-weight: 600; color: var(--text-secondary); margin-bottom: 10px; }
.solver-textarea {
  width: 100%;
  background: var(--bg-base);
  border: 1px solid var(--glass-border);
  border-radius: 12px;
  padding: 14px;
  color: var(--text-primary);
  font-family: var(--font-body); font-size: 0.9375rem;
  resize: vertical; min-height: 100px;
  outline: none; line-height: 1.6;
  transition: border-color 0.2s, box-shadow 0.2s;
}
.solver-textarea:focus { border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-glow); }
.solver-textarea::placeholder { color: var(--text-dim); }
.solver-examples { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 10px; }
.solver-example {
  font-size: 0.75rem; padding: 5px 11px; border-radius: 99px;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  color: var(--text-secondary); cursor: pointer; transition: all 0.2s;
  font-family: var(--font-body);
}
.solver-example:hover { border-color: var(--accent); color: var(--accent-light); }
.solver-solve-btn {
  width: 100%; padding: 14px;
  background: linear-gradient(135deg, var(--accent), #5B21B6);
  border: none; border-radius: 14px;
  color: white; font-family: var(--font-display); font-size: 1rem; font-weight: 700;
  cursor: pointer; margin-top: 14px;
  box-shadow: 0 8px 24px var(--accent-glow);
  transition: all 0.2s;
}
.solver-solve-btn:hover { transform: translateY(-2px); box-shadow: 0 12px 30px var(--accent-glow); }
.solver-solve-btn:active { transform: scale(0.98); }
.solver-solve-btn:disabled { opacity: 0.6; cursor: not-allowed; transform: none; }

.solver-result {
  display: none;
  background: var(--glass-bg);
  backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  border-radius: 20px; padding: 20px;
  margin-bottom: 20px;
}
.solver-result.show { display: block; animation: fadeSlideIn 0.3s var(--ease-out); }
.result-header { display: flex; align-items: center; gap: 10px; margin-bottom: 14px; }
.result-badge { padding: 4px 12px; border-radius: 99px; font-size: 0.75rem; font-weight: 700; }
.result-badge.rule { background: rgba(16,185,129,0.15); color: var(--green); border: 1px solid rgba(16,185,129,0.25); }
.result-badge.ai { background: rgba(124,58,237,0.15); color: var(--accent-light); border: 1px solid rgba(124,58,237,0.25); }
.result-title { font-family: var(--font-display); font-size: 1rem; font-weight: 700; }
.result-answer {
  background: var(--bg-elevated);
  border: 1px solid var(--glass-border);
  border-radius: 12px; padding: 16px;
  font-family: var(--font-mono); font-size: 1.1rem; font-weight: 700;
  color: var(--accent-light);
  margin-bottom: 14px;
  text-align: center;
}
.result-steps { display: flex; flex-direction: column; gap: 8px; }
.result-step {
  display: flex; gap: 10px; align-items: flex-start;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  border-radius: 10px; padding: 10px 12px;
}
.result-step-num {
  width: 22px; height: 22px; border-radius: 6px;
  background: var(--accent); color: white;
  font-size: 0.6875rem; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0; margin-top: 1px;
}
.result-step-text { font-size: 0.875rem; color: var(--text-primary); line-height: 1.5; }
.result-step-expr { font-family: var(--font-mono); font-size: 0.875rem; color: var(--accent-light); font-weight: 600; }

/* AI Key Modal */
.ai-key-card {
  background: rgba(124,58,237,0.06);
  border: 1px solid rgba(124,58,237,0.2);
  border-radius: 16px; padding: 18px;
  margin-bottom: 14px;
}
.ai-key-title { font-family: var(--font-display); font-size: 1rem; font-weight: 700; margin-bottom: 6px; }
.ai-key-sub { font-size: 0.875rem; color: var(--text-secondary); margin-bottom: 14px; line-height: 1.6; }
.ai-key-options { display: flex; flex-direction: column; gap: 8px; }
.ai-key-option {
  display: flex; align-items: center; gap: 12px;
  background: var(--glass-bg); border: 1px solid var(--glass-border);
  border-radius: 12px; padding: 12px 14px; cursor: pointer;
  transition: all 0.2s;
}
.ai-key-option:hover { border-color: var(--accent); background: rgba(124,58,237,0.08); }
.ai-key-option-icon { font-size: 24px; flex-shrink: 0; }
.ai-key-option-name { font-weight: 600; font-size: 0.875rem; }
.ai-key-option-desc { font-size: 0.75rem; color: var(--text-secondary); }

/* ═══════════════════════════════════════════════════════════════
   BOOKMARKS PAGE
═══════════════════════════════════════════════════════════════ */
.page-header { padding: 24px 16px 16px; }
.page-title { font-family: var(--font-display); font-size: 1.5rem; font-weight: 800; margin-bottom: 4px; }
.page-sub { color: var(--text-secondary); font-size: 0.875rem; }

/* ═══════════════════════════════════════════════════════════════
   SETTINGS PAGE
═══════════════════════════════════════════════════════════════ */
.settings-section { padding: 0 16px 20px; }
.settings-group { margin-bottom: 20px; }
.settings-group-title { font-size: 0.6875rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase; color: var(--text-dim); padding: 14px 4px 8px; }
.settings-item {
  display: flex; align-items: center; justify-content: space-between;
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 14px; padding: 14px 16px;
  margin-bottom: 6px; cursor: pointer; transition: all 0.2s;
}
.settings-item:hover { background: var(--glass-bg-hover); }
.settings-item-left { display: flex; align-items: center; gap: 12px; }
.settings-item-icon { font-size: 20px; width: 28px; text-align: center; }
.settings-item-name { font-weight: 600; font-size: 0.9375rem; }
.settings-item-sub { font-size: 0.75rem; color: var(--text-secondary); margin-top: 1px; }
.toggle {
  width: 44px; height: 24px; border-radius: 99px;
  background: var(--glass-border); position: relative;
  cursor: pointer; transition: background 0.3s; flex-shrink: 0;
  border: none;
}
.toggle.on { background: var(--accent); }
.toggle::after {
  content: '';
  position: absolute;
  width: 18px; height: 18px; border-radius: 50%;
  background: white; top: 3px; left: 3px;
  transition: transform 0.3s var(--ease-spring);
  box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}
.toggle.on::after { transform: translateX(20px); }

/* ═══════════════════════════════════════════════════════════════
   ANIMATIONS
═══════════════════════════════════════════════════════════════ */
@keyframes cardEntrance {
  from { opacity: 0; transform: translateY(16px); }
  to   { opacity: 1; transform: translateY(0); }
}
@keyframes fadeSlideIn {
  from { opacity: 0; transform: translateY(8px); }
  to   { opacity: 1; transform: translateY(0); }
}
@keyframes modalSlideUp {
  from { opacity: 0; transform: translateY(60px) scale(0.97); }
  to   { opacity: 1; transform: translateY(0) scale(1); }
}
@keyframes shimmer {
  from { background-position: -200% 0; }
  to   { background-position: 200% 0; }
}
@keyframes spin { to { transform: rotate(360deg); } }
@keyframes confettiFall {
  0%   { transform: translateY(-10px) rotate(0deg); opacity: 1; }
  100% { transform: translateY(100px) rotate(720deg); opacity: 0; }
}
@keyframes pulse-glow {
  0%,100% { box-shadow: 0 0 0 0 var(--accent-glow); }
  50%      { box-shadow: 0 0 0 8px transparent; }
}

.skeleton {
  background: linear-gradient(90deg, var(--skeleton-from) 25%, var(--skeleton-to) 50%, var(--skeleton-from) 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: 8px;
}

.spinner {
  width: 20px; height: 20px; border-radius: 50%;
  border: 2px solid rgba(255,255,255,0.3);
  border-top-color: white;
  animation: spin 0.7s linear infinite;
  display: inline-block;
}

/* ═══════════════════════════════════════════════════════════════
   CONFETTI
═══════════════════════════════════════════════════════════════ */
.confetti-piece {
  position: fixed;
  width: 8px; height: 8px;
  border-radius: 2px;
  pointer-events: none;
  z-index: 9999;
  animation: confettiFall 0.9s ease-out forwards;
}

/* ═══════════════════════════════════════════════════════════════
   RESPONSIVE — DESKTOP
═══════════════════════════════════════════════════════════════ */
@media (min-width: 768px) {
  #top-nav { display: flex; }
  #bottom-nav { display: none; }
  #mobile-search { display: none; }
  #app { padding-top: 64px; padding-bottom: 0; }
  #hero { padding: 60px 40px 40px; }
  .filters-section { padding: 0 40px 20px; }
  #formula-grid { padding: 8px 40px 40px; }
  .solver-page { padding: 40px; max-width: 720px; margin: 0 auto; }
  .settings-section { padding: 0 40px 40px; }
  .page-header { padding: 40px 40px 20px; }
}
@media (min-width: 1280px) {
  #formula-grid { grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); }
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.1ms !important; }
}

/* ═══════════════════════════════════════════════════════════════
   VIDEOS PAGE
═══════════════════════════════════════════════════════════════ */
.videos-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 16px;
  padding: 0 16px 32px;
}
.video-card {
  background: var(--glass-bg);
  border: 1px solid var(--glass-border);
  border-radius: 16px;
  overflow: hidden;
  transition: transform 0.18s, border-color 0.18s;
}
.video-card:hover { transform: translateY(-2px); border-color: rgba(124,58,237,0.35); }

.video-thumb-wrap { position: relative; aspect-ratio: 16/9; overflow: hidden; background: rgba(255,255,255,0.04); }
.video-thumb { width: 100%; height: 100%; object-fit: cover; display: block; transition: opacity 0.3s; }
.video-thumb-placeholder { width:100%;height:100%;display:flex;align-items:center;justify-content:center;font-size:2rem;color:var(--accent-light); }
.video-play-overlay {
  position: absolute; inset: 0; display: flex; align-items: center; justify-content: center;
  background: rgba(0,0,0,0); color: #fff; font-size: 2.25rem; opacity: 0;
  transition: opacity 0.2s, background 0.2s; cursor: pointer; text-decoration: none;
}
.video-thumb-wrap:hover .video-play-overlay { opacity: 1; background: rgba(0,0,0,0.45); }

.video-badge-community, .video-badge-pending {
  position: absolute; top: 8px; left: 8px; padding: 2px 8px; border-radius: 10px;
  font-size: 0.65rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.5px;
}
.video-badge-community { background: rgba(124,58,237,0.7); color: #fff; }
.video-badge-pending   { background: rgba(245,158,11,0.8); color: #fff; }

.video-card-body { padding: 12px 14px 14px; }
.video-card-title { font-weight: 600; font-size: 0.875rem; line-height: 1.4; margin-bottom: 4px; color: var(--text-primary); display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
.video-card-meta  { font-size: 0.75rem; color: var(--text-secondary); margin-bottom: 2px; }
.video-card-sub   { font-size: 0.7rem; color: var(--text-dim); margin-bottom: 10px; }

.video-card-actions { display: flex; gap: 6px; align-items: center; }
.vote-btn {
  display: inline-flex; align-items: center; gap: 4px; padding: 4px 10px;
  border-radius: 20px; border: 1px solid var(--glass-border); background: var(--glass-bg);
  color: var(--text-secondary); font-size: 0.75rem; cursor: pointer; transition: all 0.15s;
}
.vote-btn:hover { border-color: rgba(124,58,237,0.4); color: var(--text-primary); }
.vote-btn.voted, .vote-btn:disabled { opacity: 0.5; cursor: default; }
.vote-flag { padding: 4px 8px; }
.suggest-btn {
  margin-left: auto; padding: 4px 10px; border-radius: 20px; border: 1px solid rgba(124,58,237,0.3);
  background: rgba(124,58,237,0.08); color: #A78BFA; font-size: 0.7rem; cursor: pointer; transition: all 0.15s;
}
.suggest-btn:hover { background: rgba(124,58,237,0.18); }

@media (min-width: 768px) {
  .videos-grid { padding: 0 40px 40px; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); }
}
@media (min-width: 1280px) {
  .videos-grid { grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); }
}