/* FormulaTree — JEE Formula Revision */
@import url('https://fonts.googleapis.com/css2?family=Space+Mono:wght@400;700&family=DM+Sans:wght@300;400;500;600;700&display=swap');

:root {
  --bg: #0a0a0f;
  --bg2: #0f0f18;
  --bg3: #14141f;
  --surface: #1a1a2e;
  --surface2: #1f1f35;
  --border: rgba(255,255,255,0.07);
  --border2: rgba(255,255,255,0.12);
  --text: #e8e8f0;
  --text2: #9898b8;
  --text3: #6868a0;
  --accent: #7c6af7;
  --accent2: #6356d4;
  --accent-glow: rgba(124,106,247,0.15);
  --phys: #34d399;
  --math: #fbbf24;
  --chem: #fb7185;
  --phys-chem: #60a5fa;
  --inorg-chem: #a78bfa;
  --org-chem: #34d399;
  --radius: 12px;
  --radius-lg: 18px;
  --font-mono: 'Space Mono', monospace;
  --font-body: 'DM Sans', sans-serif;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 15px;
  line-height: 1.6;
  min-height: 100vh;
}

/* ── Header ── */
.header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(10,10,15,0.92);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  padding: 0 24px;
  height: 58px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text);
}

.logo-icon {
  width: 32px;
  height: 32px;
  background: var(--accent);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 16px;
}

.logo-text {
  font-family: var(--font-mono);
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.3px;
}

.logo-text span {
  color: var(--accent);
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 6px;
}

.nav-link {
  padding: 6px 14px;
  border-radius: 8px;
  text-decoration: none;
  font-size: 13.5px;
  font-weight: 500;
  color: var(--text2);
  transition: all 0.18s;
}

.nav-link:hover {
  background: var(--surface);
  color: var(--text);
}

.nav-link.active {
  background: var(--accent-glow);
  color: var(--accent);
}

.search-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text3);
  font-size: 13px;
  cursor: pointer;
  font-family: var(--font-body);
  transition: all 0.18s;
}

.search-btn:hover { border-color: var(--border2); color: var(--text2); }

.search-btn kbd {
  background: var(--bg3);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 1px 5px;
  font-family: var(--font-mono);
  font-size: 10px;
}

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

/* ── Hero ── */
.hero {
  padding: 80px 0 60px;
  text-align: center;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--accent-glow);
  border: 1px solid rgba(124,106,247,0.2);
  border-radius: 100px;
  padding: 5px 14px;
  font-size: 12px;
  color: var(--accent);
  font-weight: 500;
  margin-bottom: 24px;
  letter-spacing: 0.3px;
}

.hero h1 {
  font-size: clamp(32px, 5vw, 52px);
  font-weight: 700;
  letter-spacing: -1.5px;
  line-height: 1.1;
  margin-bottom: 16px;
}

.hero h1 span {
  background: linear-gradient(135deg, var(--accent), #b794f4);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-sub {
  font-size: 17px;
  color: var(--text2);
  max-width: 520px;
  margin: 0 auto 40px;
  font-weight: 400;
}

.stats-row {
  display: flex;
  justify-content: center;
  gap: 40px;
  flex-wrap: wrap;
}

.stat {
  text-align: center;
}

.stat-num {
  font-family: var(--font-mono);
  font-size: 28px;
  font-weight: 700;
  color: var(--text);
}

.stat-label {
  font-size: 12px;
  color: var(--text3);
  margin-top: 2px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

/* ── Subject Cards ── */
.subjects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 320px), 1fr));
  gap: 20px;
  padding: 20px 0 80px;
}

.subject-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  text-decoration: none;
  color: var(--text);
  transition: all 0.22s;
  cursor: pointer;
  display: block;
  position: relative;
  overflow: hidden;
}

.subject-card::before {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, transparent 60%, var(--card-color, var(--accent)) 200%);
  opacity: 0;
  transition: opacity 0.3s;
}

.subject-card:hover {
  border-color: var(--card-color, var(--accent));
  transform: translateY(-3px);
  box-shadow: 0 12px 40px rgba(0,0,0,0.4);
}

.subject-card:hover::before { opacity: 0.06; }

.card-header {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 16px;
}

.card-icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  flex-shrink: 0;
}

.card-title {
  font-size: 20px;
  font-weight: 700;
  letter-spacing: -0.3px;
}

.card-desc {
  font-size: 13.5px;
  color: var(--text2);
  line-height: 1.5;
  margin-bottom: 20px;
}

.card-meta {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.card-tag {
  display: flex;
  align-items: center;
  gap: 5px;
  background: var(--bg3);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 4px 10px;
  font-size: 12px;
  color: var(--text2);
  font-family: var(--font-mono);
}

/* ── Page header (subject pages) ── */
.page-header {
  padding: 48px 0 40px;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--text3);
  margin-bottom: 20px;
  flex-wrap: wrap;
}

.breadcrumb a {
  color: var(--text2);
  text-decoration: none;
  transition: color 0.15s;
}

.breadcrumb a:hover { color: var(--text); }

.breadcrumb span.sep { opacity: 0.4; }

.breadcrumb span.current { color: var(--text); }

.page-title-row {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 12px;
}

.page-icon {
  width: 52px;
  height: 52px;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 28px;
}

.page-title {
  font-size: clamp(26px, 4vw, 40px);
  font-weight: 700;
  letter-spacing: -1px;
}

.page-sub {
  color: var(--text2);
  font-size: 15px;
  margin-bottom: 24px;
}

/* ── Section tabs (Chemistry) ── */
.section-tabs {
  display: flex;
  gap: 8px;
  padding: 20px 0;
  flex-wrap: wrap;
}

.section-tab {
  padding: 10px 22px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text2);
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.18s;
  font-family: var(--font-body);
}

.section-tab:hover { border-color: var(--border2); color: var(--text); }

.section-tab.active {
  border-color: var(--tab-color, var(--accent));
  background: rgba(124,106,247,0.08);
  color: var(--tab-color, var(--accent));
}

/* ── Chapter list ── */
.chapters-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 14px;
  padding-bottom: 60px;
}

.chapter-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  cursor: pointer;
  transition: all 0.18s;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.chapter-card:hover {
  border-color: var(--chapter-color, var(--accent));
  background: var(--surface2);
  transform: translateX(3px);
}

.chapter-name {
  font-size: 14.5px;
  font-weight: 600;
}

.chapter-count {
  font-size: 12px;
  color: var(--text3);
  font-family: var(--font-mono);
  background: var(--bg3);
  border-radius: 5px;
  padding: 3px 8px;
  flex-shrink: 0;
}

/* ── Back button ── */
.back-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text2);
  font-size: 13.5px;
  cursor: pointer;
  font-family: var(--font-body);
  transition: all 0.18s;
  margin-bottom: 24px;
}

.back-btn:hover { border-color: var(--border2); color: var(--text); }

/* ── Formula cards ── */
.formulas-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
  padding-bottom: 80px;
}

.formula-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color 0.18s;
}

.formula-card:hover { border-color: var(--border2); }
.formula-card.open { border-color: var(--accent); }

.formula-header {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 16px 20px;
  cursor: pointer;
  user-select: none;
}

.formula-num {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--text3);
  min-width: 26px;
}

.formula-name {
  font-size: 15px;
  font-weight: 600;
  flex: 1;
}

.formula-eq-preview {
  font-family: var(--font-mono);
  font-size: 12.5px;
  color: var(--accent);
  background: var(--accent-glow);
  border-radius: 6px;
  padding: 4px 10px;
  max-width: 280px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.formula-toggle {
  width: 22px;
  height: 22px;
  color: var(--text3);
  transition: transform 0.2s;
  flex-shrink: 0;
}

.formula-card.open .formula-toggle { transform: rotate(180deg); }

.formula-body {
  padding: 0 20px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, padding 0.3s ease;
}

.formula-card.open .formula-body {
  max-height: 1200px;
  padding: 0 20px 20px;
}

.formula-eq-full {
  font-family: var(--font-mono);
  font-size: 15px;
  color: var(--accent);
  background: var(--bg2);
  border: 1px solid rgba(124,106,247,0.2);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin-bottom: 16px;
  word-break: break-all;
  line-height: 1.7;
}

.formula-section {
  margin-bottom: 14px;
}

.formula-section-label {
  font-size: 10.5px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--text3);
  margin-bottom: 6px;
}

.formula-section-text {
  font-size: 14px;
  color: var(--text2);
  line-height: 1.6;
}

.pills-row {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.pill {
  padding: 4px 12px;
  border-radius: 100px;
  font-size: 12.5px;
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text2);
  cursor: pointer;
  transition: all 0.15s;
  font-family: var(--font-body);
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.pill:hover { border-color: var(--border2); color: var(--text); }

.pill.linked {
  background: rgba(124,106,247,0.08);
  border-color: rgba(124,106,247,0.25);
  color: var(--accent);
}

.pill.linked:hover {
  background: rgba(124,106,247,0.15);
}

.jee-pill {
  background: rgba(251,191,36,0.06);
  border: 1px solid rgba(251,191,36,0.15);
  color: var(--math);
  padding: 3px 10px;
  border-radius: 6px;
  font-size: 12.5px;
}

/* ── Search modal ── */
.search-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.7);
  backdrop-filter: blur(8px);
  z-index: 1000;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 80px;
}

.search-overlay.open { display: flex; }

.search-modal {
  background: var(--surface);
  border: 1px solid var(--border2);
  border-radius: var(--radius-lg);
  width: min(640px, 90vw);
  box-shadow: 0 32px 80px rgba(0,0,0,0.6);
  overflow: hidden;
  animation: slideDown 0.18s ease;
}

@keyframes slideDown {
  from { transform: translateY(-20px); opacity: 0; }
  to { transform: translateY(0); opacity: 1; }
}

.search-input-row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
}

.search-input-row svg { color: var(--text3); flex-shrink: 0; }

.search-input {
  flex: 1;
  background: none;
  border: none;
  outline: none;
  font-size: 16px;
  color: var(--text);
  font-family: var(--font-body);
}

.search-input::placeholder { color: var(--text3); }

.search-results {
  max-height: 420px;
  overflow-y: auto;
}

.search-result {
  padding: 12px 18px;
  cursor: pointer;
  transition: background 0.12s;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 14px;
}

.search-result:hover { background: var(--surface2); }

.search-result-icon {
  font-size: 18px;
  width: 28px;
  text-align: center;
  flex-shrink: 0;
}

.search-result-name { font-size: 14.5px; font-weight: 600; }
.search-result-eq { font-family: var(--font-mono); font-size: 12px; color: var(--accent); }
.search-result-path { font-size: 12px; color: var(--text3); }

.search-empty {
  padding: 32px 20px;
  text-align: center;
  color: var(--text3);
  font-size: 14px;
}

/* ── Animations ── */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(14px); }
  to { opacity: 1; transform: translateY(0); }
}

.fade-up {
  animation: fadeUp 0.4s ease both;
}

.fade-up:nth-child(1) { animation-delay: 0.05s; }
.fade-up:nth-child(2) { animation-delay: 0.1s; }
.fade-up:nth-child(3) { animation-delay: 0.15s; }
.fade-up:nth-child(4) { animation-delay: 0.2s; }
.fade-up:nth-child(5) { animation-delay: 0.25s; }
.fade-up:nth-child(6) { animation-delay: 0.3s; }
.fade-up:nth-child(7) { animation-delay: 0.35s; }
.fade-up:nth-child(8) { animation-delay: 0.4s; }
.fade-up:nth-child(9) { animation-delay: 0.45s; }

/* ── Pill Popup ── */
/* FIX 5: overlay hidden by default, shown when .open added */
.pill-popup-overlay {
  position: fixed;
  inset: 0;
  z-index: 500;
  display: none;
  background: rgba(0,0,0,0.01); /* transparent but catches clicks */
}
.pill-popup-overlay.open {
  display: block;
}

.pill-popup {
  position: fixed;
  background: var(--surface);
  border: 1px solid var(--border2);
  border-radius: var(--radius);
  padding: 16px 18px;
  max-width: 340px;
  box-shadow: 0 16px 48px rgba(0,0,0,0.55);
  z-index: 501;
  animation: fadeUp 0.15s ease both;
  pointer-events: all;
}

.pill-popup-title {
  font-size: 13.5px;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.pill-popup-close {
  width: 20px;
  height: 20px;
  border-radius: 4px;
  background: var(--bg3);
  border: 1px solid var(--border);
  color: var(--text3);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  flex-shrink: 0;
  line-height: 1;
  font-family: var(--font-body);
}
.pill-popup-close:hover { color: var(--text); }

.pill-popup-body {
  font-size: 13px;
  color: var(--text2);
  line-height: 1.6;
}

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--surface2); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--border2); }

/* ── Footer ── */
.footer {
  border-top: 1px solid var(--border);
  padding: 32px 0;
  text-align: center;
  color: var(--text3);
  font-size: 13px;
}

/* ── Responsive ── */
@media (max-width: 768px) {
  .subjects-grid { grid-template-columns: 1fr; }
  .chapters-grid { grid-template-columns: 1fr; }
  .header-nav { display: none; }
  .formula-eq-preview { display: none; }
  .hero { padding: 50px 0 40px; }
  .stats-row { gap: 24px; }
}