/* ============================================
   ScienceVerse — Science Portal Styles
   Design: Deep Space + Neon Science Aesthetic
   Fonts: Syne (Display) + Bricolage Grotesque (Body)
   Palette: Volcanic Glass + Acid Neon accents
   ============================================ */

:root {
  --bg-primary: #080B14;
  --bg-secondary: #0D1220;
  --bg-card: #111827;
  --bg-card-hover: #161f35;
  --border: rgba(99, 179, 237, 0.12);
  --border-bright: rgba(99, 179, 237, 0.3);

  --text-primary: #E8EDF5;
  --text-secondary: #8B9BB4;
  --text-muted: #4A5568;

  --accent-blue: #63B3ED;
  --accent-purple: #B794F4;
  --accent-green: #68D391;
  --accent-yellow: #F6E05E;
  --accent-red: #FC8181;
  --accent-cyan: #76E4F7;

  --physics-color: #63B3ED;
  --chemistry-color: #B794F4;
  --biology-color: #68D391;

  --glow-blue: rgba(99, 179, 237, 0.15);
  --glow-purple: rgba(183, 148, 244, 0.15);
  --glow-green: rgba(104, 211, 145, 0.15);

  --font-display: 'Syne', sans-serif;
  --font-body: 'Bricolage Grotesque', sans-serif;
  --font-mono: 'Space Mono', monospace;

  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-xl: 28px;

  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}

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

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
}

a { text-decoration: none; color: inherit; }
button { cursor: pointer; border: none; background: none; font-family: inherit; }
ul { list-style: none; }

/* ── Particle Canvas ── */
#particleCanvas {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  pointer-events: none;
  z-index: 0;
  opacity: 0.4;
}

/* ── Container ── */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--bg-primary); }
::-webkit-scrollbar-thumb { background: var(--accent-blue); border-radius: 3px; }

/* ============================================
   NAVBAR
   ============================================ */
.navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  background: rgba(8, 11, 20, 0.85);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  transition: var(--transition);
}

.navbar.scrolled {
  background: rgba(8, 11, 20, 0.97);
  border-bottom-color: var(--border-bright);
}

.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
  height: 68px;
  display: flex;
  align-items: center;
  gap: 32px;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-family: var(--font-display);
  font-weight: 800;
  font-size: 1.25rem;
  color: var(--text-primary);
  flex-shrink: 0;
}

.logo-icon {
  font-size: 1.5rem;
  filter: drop-shadow(0 0 8px var(--accent-blue));
  animation: spin-slow 8s linear infinite;
}

@keyframes spin-slow {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

.nav-links {
  display: flex;
  gap: 4px;
  margin-left: auto;
}

.nav-link {
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: var(--transition);
}

.nav-link:hover {
  color: var(--text-primary);
  background: rgba(99, 179, 237, 0.08);
}

.nav-search-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 18px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-family: var(--font-body);
  transition: var(--transition);
  background: rgba(255,255,255,0.03);
}

.nav-search-btn:hover {
  border-color: var(--accent-blue);
  color: var(--accent-blue);
  background: var(--glow-blue);
}

.hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 8px;
  margin-left: auto;
}

.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text-secondary);
  border-radius: 2px;
  transition: var(--transition);
}

.mobile-menu {
  display: none;
  flex-direction: column;
  padding: 12px 24px 16px;
  border-top: 1px solid var(--border);
  gap: 4px;
}

.mobile-menu a {
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.95rem;
  transition: var(--transition);
}

.mobile-menu a:hover {
  color: var(--text-primary);
  background: rgba(99, 179, 237, 0.08);
}

.mobile-menu.open { display: flex; }

/* ============================================
   SEARCH OVERLAY
   ============================================ */
.search-overlay {
  position: fixed;
  inset: 0;
  z-index: 2000;
  background: rgba(8, 11, 20, 0.96);
  backdrop-filter: blur(20px);
  display: flex;
  flex-direction: column;
  align-items: center;
  padding-top: 120px;
  opacity: 0;
  pointer-events: none;
  transition: var(--transition);
}

.search-overlay.open {
  opacity: 1;
  pointer-events: all;
}

.search-box {
  display: flex;
  align-items: center;
  width: 100%;
  max-width: 640px;
  background: var(--bg-card);
  border: 1px solid var(--border-bright);
  border-radius: var(--radius-lg);
  padding: 4px 4px 4px 24px;
  gap: 12px;
}

#searchInput {
  flex: 1;
  background: none;
  border: none;
  outline: none;
  font-family: var(--font-body);
  font-size: 1.1rem;
  color: var(--text-primary);
  padding: 12px 0;
}

#searchInput::placeholder { color: var(--text-muted); }

.search-close {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-sm);
  background: rgba(255,255,255,0.06);
  color: var(--text-secondary);
  font-size: 1rem;
  transition: var(--transition);
}

.search-close:hover { background: rgba(255,255,255,0.12); color: var(--text-primary); }

.search-results {
  width: 100%;
  max-width: 640px;
  margin-top: 16px;
  display: flex;
  flex-direction: column;
  gap: 8px;
  max-height: 400px;
  overflow-y: auto;
}

.search-result-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 14px 18px;
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 14px;
}

.search-result-item:hover {
  border-color: var(--accent-blue);
  background: var(--bg-card-hover);
}

.search-result-subject {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: 4px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  flex-shrink: 0;
}

.search-result-title { font-weight: 500; font-size: 0.95rem; }
.search-result-grade { font-size: 0.8rem; color: var(--text-muted); margin-left: auto; }

/* ============================================
   HERO
   ============================================ */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding: 100px 24px 60px;
  max-width: 1200px;
  margin: 0 auto;
  gap: 60px;
  position: relative;
  z-index: 1;
}

.hero-content {
  flex: 1;
  max-width: 580px;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 16px;
  border-radius: 100px;
  border: 1px solid rgba(99, 179, 237, 0.3);
  background: rgba(99, 179, 237, 0.08);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-blue);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: 24px;
  animation: fadeInUp 0.6s ease both;
}

.hero-title {
  font-family: var(--font-display);
  font-size: clamp(2.8rem, 6vw, 4.5rem);
  font-weight: 800;
  line-height: 1.05;
  letter-spacing: -0.02em;
  margin-bottom: 20px;
  animation: fadeInUp 0.6s 0.1s ease both;
}

.gradient-text {
  background: linear-gradient(135deg, var(--accent-blue) 0%, var(--accent-purple) 50%, var(--accent-cyan) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-subtitle {
  font-size: 1.05rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 36px;
  animation: fadeInUp 0.6s 0.2s ease both;
}

.hero-actions {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 48px;
  animation: fadeInUp 0.6s 0.3s ease both;
}

.btn-primary {
  padding: 14px 32px;
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: #fff;
  font-weight: 700;
  font-size: 0.95rem;
  font-family: var(--font-display);
  transition: var(--transition);
  box-shadow: 0 0 30px rgba(99, 179, 237, 0.3);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 0 50px rgba(99, 179, 237, 0.5);
}

.btn-secondary {
  padding: 14px 32px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-bright);
  color: var(--text-primary);
  font-weight: 600;
  font-size: 0.95rem;
  font-family: var(--font-display);
  transition: var(--transition);
  background: rgba(255,255,255,0.03);
}

.btn-secondary:hover {
  border-color: var(--accent-purple);
  background: var(--glow-purple);
  color: var(--accent-purple);
}

.hero-stats {
  display: flex;
  align-items: center;
  gap: 24px;
  animation: fadeInUp 0.6s 0.4s ease both;
}

.stat { display: flex; flex-direction: column; }
.stat-num {
  font-family: var(--font-display);
  font-size: 1.8rem;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1;
}
.stat-label { font-size: 0.75rem; color: var(--text-muted); margin-top: 2px; }
.stat-divider { width: 1px; height: 36px; background: var(--border); }

/* ── Atom Visual ── */
.hero-visual {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  min-height: 400px;
  animation: fadeIn 1s 0.5s ease both;
}

.atom-container {
  position: relative;
  width: 280px;
  height: 280px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.nucleus {
  position: absolute;
  width: 70px;
  height: 70px;
  border-radius: 50%;
  background: radial-gradient(circle, var(--accent-blue), var(--accent-purple));
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 0 40px rgba(99, 179, 237, 0.6), 0 0 80px rgba(183, 148, 244, 0.3);
  z-index: 2;
}

.nucleus-core { font-size: 2rem; }

.orbit {
  position: absolute;
  border-radius: 50%;
  border: 1px solid rgba(99, 179, 237, 0.25);
}

.orbit-1 { width: 140px; height: 140px; animation: orbit-spin 3s linear infinite; }
.orbit-2 { width: 200px; height: 200px; animation: orbit-spin 5s linear infinite reverse; transform: rotate(60deg); }
.orbit-3 { width: 260px; height: 260px; animation: orbit-spin 7s linear infinite; transform: rotate(120deg); }

@keyframes orbit-spin {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

.orbit-2 { animation: orbit-spin2 5s linear infinite reverse; }
@keyframes orbit-spin2 {
  from { transform: rotate(60deg); }
  to { transform: rotate(420deg); }
}

.orbit-3 { animation: orbit-spin3 7s linear infinite; }
@keyframes orbit-spin3 {
  from { transform: rotate(120deg); }
  to { transform: rotate(480deg); }
}

.electron {
  position: absolute;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  top: -5px;
  left: 50%;
  transform: translateX(-50%);
}

.e1 { background: var(--accent-blue); box-shadow: 0 0 10px var(--accent-blue); }
.e2 { background: var(--accent-purple); box-shadow: 0 0 10px var(--accent-purple); }
.e3 { background: var(--accent-cyan); box-shadow: 0 0 10px var(--accent-cyan); }

.floating-formula {
  position: absolute;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--accent-blue);
  background: rgba(99, 179, 237, 0.08);
  border: 1px solid rgba(99, 179, 237, 0.2);
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  white-space: nowrap;
  animation: float 4s ease-in-out infinite;
}

.f1 { top: 5%; right: 5%; animation-delay: 0s; color: var(--accent-blue); }
.f2 { top: 25%; left: -5%; animation-delay: 0.8s; color: var(--accent-purple); border-color: rgba(183,148,244,0.2); background: rgba(183,148,244,0.08); }
.f3 { bottom: 20%; right: 0%; animation-delay: 1.6s; color: var(--accent-green); border-color: rgba(104,211,145,0.2); background: rgba(104,211,145,0.08); }
.f4 { bottom: 5%; left: 5%; animation-delay: 2.4s; color: var(--accent-yellow); border-color: rgba(246,224,94,0.2); background: rgba(246,224,94,0.08); }
.f5 { top: 55%; right: -5%; animation-delay: 3.2s; color: var(--accent-cyan); border-color: rgba(118,228,247,0.2); background: rgba(118,228,247,0.08); }

@keyframes float {
  0%, 100% { transform: translateY(0px); }
  50% { transform: translateY(-12px); }
}

/* ============================================
   SECTION COMMONS
   ============================================ */
.section-header {
  text-align: center;
  margin-bottom: 48px;
}

.section-tag {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent-blue);
  margin-bottom: 12px;
}

.section-title {
  font-family: var(--font-display);
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: 14px;
}

.section-desc {
  font-size: 1rem;
  color: var(--text-secondary);
  max-width: 520px;
  margin: 0 auto;
  line-height: 1.7;
}

/* ============================================
   GRADES SECTION
   ============================================ */
.grades-section {
  padding: 100px 0;
  position: relative;
  z-index: 1;
}

.grade-cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.grade-card {
  position: relative;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: 36px 28px;
  cursor: pointer;
  transition: var(--transition);
  overflow: hidden;
}

.grade-card:hover {
  border-color: var(--border-bright);
  transform: translateY(-6px);
  background: var(--bg-card-hover);
}

.grade-card.featured {
  border-color: rgba(183, 148, 244, 0.3);
  background: linear-gradient(135deg, rgba(183,148,244,0.05), rgba(99,179,237,0.05));
}

.grade-card.active {
  border-color: var(--accent-blue);
  box-shadow: 0 0 40px rgba(99, 179, 237, 0.2);
}

.grade-glow {
  position: absolute;
  top: -40px;
  right: -40px;
  width: 160px;
  height: 160px;
  border-radius: 50%;
  filter: blur(60px);
  opacity: 0.4;
  pointer-events: none;
}

.glow-blue { background: var(--accent-blue); }
.glow-purple { background: var(--accent-purple); }
.glow-green { background: var(--accent-green); }

.grade-badge-top {
  position: absolute;
  top: 16px;
  right: 16px;
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent-purple);
  background: rgba(183,148,244,0.12);
  border: 1px solid rgba(183,148,244,0.25);
  padding: 4px 10px;
  border-radius: 100px;
}

.grade-icon { font-size: 2.5rem; margin-bottom: 16px; }

.grade-num {
  font-family: var(--font-display);
  font-size: 1.6rem;
  font-weight: 800;
  margin-bottom: 4px;
}

.grade-board {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 20px;
}

.grade-subjects-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 20px;
}

.grade-subjects-list li {
  font-size: 0.9rem;
  color: var(--text-secondary);
  display: flex;
  align-items: center;
  gap: 8px;
}

.grade-topics-count {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent-blue);
  margin-bottom: 16px;
}

.grade-btn {
  font-weight: 700;
  font-size: 0.9rem;
  color: var(--text-secondary);
  transition: var(--transition);
}

.grade-card:hover .grade-btn { color: var(--accent-blue); }

/* ============================================
   SUBJECTS / TOPICS SECTION
   ============================================ */
.subjects-section {
  padding: 80px 0 100px;
  position: relative;
  z-index: 1;
}

.filter-bar {
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-bottom: 40px;
}

.grade-filters, .subject-filters {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.filter-btn {
  padding: 8px 20px;
  border-radius: 100px;
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 500;
  font-family: var(--font-body);
  transition: var(--transition);
  background: rgba(255,255,255,0.02);
}

.filter-btn:hover, .filter-btn.active {
  border-color: var(--accent-blue);
  color: var(--accent-blue);
  background: var(--glow-blue);
}

.subject-btn {
  padding: 8px 20px;
  border-radius: 100px;
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 600;
  font-family: var(--font-body);
  transition: var(--transition);
  background: rgba(255,255,255,0.02);
}

.subject-btn.active, .subject-btn:hover { border-color: var(--border-bright); color: var(--text-primary); }
.physics-btn.active { border-color: var(--physics-color); color: var(--physics-color); background: rgba(99,179,237,0.08); }
.chemistry-btn.active { border-color: var(--chemistry-color); color: var(--chemistry-color); background: rgba(183,148,244,0.08); }
.biology-btn.active { border-color: var(--biology-color); color: var(--biology-color); background: rgba(104,211,145,0.08); }

/* ── Topics Grid ── */
.topics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 20px;
}

.topic-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  cursor: pointer;
  transition: var(--transition);
  position: relative;
  overflow: hidden;
  animation: fadeInUp 0.4s ease both;
}

.topic-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
}

.topic-card.physics::before { background: linear-gradient(90deg, var(--physics-color), var(--accent-cyan)); }
.topic-card.chemistry::before { background: linear-gradient(90deg, var(--chemistry-color), var(--accent-blue)); }
.topic-card.biology::before { background: linear-gradient(90deg, var(--biology-color), var(--accent-yellow)); }

.topic-card:hover {
  border-color: var(--border-bright);
  transform: translateY(-4px);
  background: var(--bg-card-hover);
}

.topic-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: 12px;
  gap: 12px;
}

.topic-subject-badge {
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 4px 10px;
  border-radius: 100px;
}

.badge-physics { background: rgba(99,179,237,0.12); color: var(--physics-color); }
.badge-chemistry { background: rgba(183,148,244,0.12); color: var(--chemistry-color); }
.badge-biology { background: rgba(104,211,145,0.12); color: var(--biology-color); }

.topic-grade-badge {
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  padding: 4px 10px;
  border-radius: 100px;
  border: 1px solid var(--border);
}

.topic-title {
  font-family: var(--font-display);
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 8px;
  line-height: 1.3;
}

.topic-desc {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 16px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.topic-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.topic-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.topic-tag {
  font-size: 0.7rem;
  color: var(--text-muted);
  background: rgba(255,255,255,0.04);
  padding: 3px 8px;
  border-radius: 4px;
}

.topic-arrow {
  color: var(--text-muted);
  font-size: 1rem;
  transition: var(--transition);
}

.topic-card:hover .topic-arrow { color: var(--accent-blue); transform: translateX(4px); }

/* ── No Results ── */
.no-results {
  grid-column: 1 / -1;
  text-align: center;
  padding: 60px 20px;
  color: var(--text-muted);
}

.no-results-icon { font-size: 3rem; margin-bottom: 16px; }
.no-results h3 { font-family: var(--font-display); font-size: 1.2rem; margin-bottom: 8px; color: var(--text-secondary); }

/* ============================================
   MODAL
   ============================================ */
.modal-overlay {
  position: fixed;
  inset: 0;
  z-index: 3000;
  background: rgba(8, 11, 20, 0.9);
  backdrop-filter: blur(12px);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  opacity: 0;
  pointer-events: none;
  transition: var(--transition);
}

.modal-overlay.open {
  opacity: 1;
  pointer-events: all;
}

.modal {
  background: var(--bg-card);
  border: 1px solid var(--border-bright);
  border-radius: var(--radius-xl);
  width: 100%;
  max-width: 680px;
  max-height: 85vh;
  overflow-y: auto;
  position: relative;
  transform: scale(0.95) translateY(20px);
  transition: var(--transition);
}

.modal-overlay.open .modal {
  transform: scale(1) translateY(0);
}

.modal-close {
  position: absolute;
  top: 20px;
  right: 20px;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  background: rgba(255,255,255,0.06);
  color: var(--text-secondary);
  font-size: 0.9rem;
  transition: var(--transition);
  z-index: 1;
}

.modal-close:hover { background: rgba(255,255,255,0.12); color: var(--text-primary); }

.modal-header {
  padding: 32px 32px 24px;
  border-bottom: 1px solid var(--border);
}

.modal-subject-badge {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 5px 12px;
  border-radius: 100px;
  display: inline-block;
  margin-bottom: 14px;
}

.modal-title {
  font-family: var(--font-display);
  font-size: 1.6rem;
  font-weight: 800;
  margin-bottom: 10px;
  line-height: 1.2;
}

.modal-meta {
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
}

.modal-body {
  padding: 28px 32px 32px;
}

.modal-section {
  margin-bottom: 28px;
}

.modal-section-title {
  font-family: var(--font-display);
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent-blue);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.modal-section-title::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--border);
}

.modal-text {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.75;
}

.modal-formula-box {
  background: rgba(99,179,237,0.06);
  border: 1px solid rgba(99,179,237,0.2);
  border-radius: var(--radius-md);
  padding: 16px 20px;
  font-family: var(--font-mono);
  font-size: 1rem;
  color: var(--accent-blue);
  margin: 12px 0;
  text-align: center;
  letter-spacing: 0.05em;
}

.modal-points {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.modal-point {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.modal-point-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent-blue);
  margin-top: 7px;
  flex-shrink: 0;
}

.modal-tags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.modal-tag {
  font-size: 0.8rem;
  padding: 5px 12px;
  border-radius: var(--radius-sm);
  background: rgba(255,255,255,0.05);
  border: 1px solid var(--border);
  color: var(--text-secondary);
}

/* ============================================
   FORMULA SECTION
   ============================================ */
.formulas-section {
  padding: 100px 0;
  position: relative;
  z-index: 1;
  background: linear-gradient(180deg, transparent, rgba(99,179,237,0.03), transparent);
}

.formula-tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 36px;
  justify-content: center;
}

.ftab {
  padding: 10px 28px;
  border-radius: 100px;
  border: 1px solid var(--border);
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 600;
  font-family: var(--font-body);
  transition: var(--transition);
  background: rgba(255,255,255,0.02);
}

.ftab.active {
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  border-color: transparent;
  color: #fff;
}

.formula-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}

.formula-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px;
  transition: var(--transition);
  animation: fadeInUp 0.3s ease both;
}

.formula-card:hover {
  border-color: var(--border-bright);
  transform: translateY(-2px);
}

.formula-name {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 10px;
}

.formula-expr {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  color: var(--accent-blue);
  margin-bottom: 8px;
  padding: 10px 14px;
  background: rgba(99,179,237,0.06);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--accent-blue);
}

.formula-expr.chem { color: var(--chemistry-color); background: rgba(183,148,244,0.06); border-left-color: var(--chemistry-color); }
.formula-expr.bio { color: var(--biology-color); background: rgba(104,211,145,0.06); border-left-color: var(--biology-color); }

.formula-desc {
  font-size: 0.82rem;
  color: var(--text-muted);
  line-height: 1.5;
}

.formula-grade {
  font-size: 0.7rem;
  color: var(--text-muted);
  margin-top: 8px;
  font-family: var(--font-mono);
}

/* ============================================
   PERIODIC TABLE SECTION
   ============================================ */
.periodic-section {
  padding: 100px 0;
  position: relative;
  z-index: 1;
}

.periodic-inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
  align-items: center;
}

.periodic-text h2 {
  font-family: var(--font-display);
  font-size: clamp(1.8rem, 3.5vw, 2.6rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin: 12px 0 16px;
  line-height: 1.15;
}

.periodic-text p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.75;
  margin-bottom: 28px;
}

.element-highlights {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.elem-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 64px;
  padding: 10px 8px;
  border-radius: var(--radius-md);
  border: 1px solid rgba(255,255,255,0.08);
  background: rgba(255,255,255,0.03);
  font-family: var(--font-mono);
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--ec);
  cursor: default;
  transition: var(--transition);
}

.elem-card:hover {
  background: rgba(255,255,255,0.07);
  transform: translateY(-3px);
  box-shadow: 0 0 20px color-mix(in srgb, var(--ec) 30%, transparent);
}

.elem-card span {
  font-size: 0.6rem;
  font-family: var(--font-body);
  color: var(--text-muted);
  margin-top: 3px;
  font-weight: 400;
}

.elem-card small {
  font-size: 0.65rem;
  color: var(--text-muted);
  font-family: var(--font-mono);
}

.mini-table {
  display: grid;
  grid-template-columns: repeat(18, 1fr);
  gap: 2px;
}

.mini-elem {
  aspect-ratio: 1;
  border-radius: 2px;
  font-size: 0.35rem;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-weight: 700;
  transition: var(--transition);
  cursor: default;
}

.mini-elem:hover { transform: scale(1.5); z-index: 10; position: relative; }

/* ============================================
   TIPS SECTION
   ============================================ */
.tips-section {
  padding: 100px 0;
  position: relative;
  z-index: 1;
}

.tips-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.tip-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  transition: var(--transition);
}

.tip-card:hover {
  border-color: var(--border-bright);
  transform: translateY(-4px);
  background: var(--bg-card-hover);
}

.tip-icon {
  font-size: 2rem;
  margin-bottom: 16px;
}

.tip-card h3 {
  font-family: var(--font-display);
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 10px;
}

.tip-card p {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ============================================
   FOOTER
   ============================================ */
.footer {
  border-top: 1px solid var(--border);
  padding: 60px 0 32px;
  position: relative;
  z-index: 1;
}

.footer-inner {
  display: flex;
  gap: 60px;
  margin-bottom: 48px;
}

.footer-brand {
  flex: 1;
}

.footer-brand .logo-icon { font-size: 1.5rem; margin-right: 8px; }
.footer-brand .logo-text {
  font-family: var(--font-display);
  font-size: 1.1rem;
  font-weight: 800;
}

.footer-brand p {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: 10px;
  line-height: 1.6;
  max-width: 240px;
}

.footer-links {
  display: flex;
  gap: 48px;
}

.footer-col {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-col h4 {
  font-family: var(--font-display);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.footer-col a {
  font-size: 0.875rem;
  color: var(--text-secondary);
  transition: var(--transition);
}

.footer-col a:hover { color: var(--accent-blue); }

.footer-bottom {
  border-top: 1px solid var(--border);
  padding-top: 24px;
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* ============================================
   ANIMATIONS
   ============================================ */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(24px); }
  to { opacity: 1; transform: translateY(0); }
}

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

.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ============================================
   RESPONSIVE
   ============================================ */
@media (max-width: 1024px) {
  .grade-cards { grid-template-columns: repeat(3, 1fr); gap: 16px; }
  .periodic-inner { grid-template-columns: 1fr; gap: 40px; }
  .tips-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
  .nav-links, .nav-search-btn { display: none; }
  .hamburger { display: flex; }

  .hero {
    flex-direction: column;
    padding: 100px 24px 60px;
    text-align: center;
    gap: 40px;
  }

  .hero-actions { justify-content: center; }
  .hero-stats { justify-content: center; }
  .hero-visual { min-height: 280px; }

  .grade-cards { grid-template-columns: 1fr; max-width: 360px; margin: 0 auto; }
  .tips-grid { grid-template-columns: 1fr; }

  .footer-inner { flex-direction: column; gap: 32px; }
  .footer-links { flex-wrap: wrap; gap: 32px; }

  .modal { margin: 16px; max-height: 90vh; }
  .modal-header, .modal-body { padding: 24px; }

  .formula-tabs { flex-wrap: wrap; }
  .filter-bar { gap: 10px; }
}

@media (max-width: 480px) {
  .hero-title { font-size: 2.2rem; }
  .section-title { font-size: 1.6rem; }
  .topics-grid { grid-template-columns: 1fr; }
  .formula-grid { grid-template-columns: 1fr; }
  .hero-stats { gap: 16px; }
  .stat-num { font-size: 1.4rem; }
}