/* ═══════════════════════════════════════════════
   药理学入门 — 全站样式
   主色调：医疗蓝绿 #0369a1
   ═══════════════════════════════════════════════ */

/* ─── 全局变量 ─── */
:root {
  --primary:        #0369a1;
  --primary-dark:   #0c4a6e;
  --primary-light:  #e0f2fe;
  --accent:         #0891b2;
  --text-main:      #1f2937;
  --text-muted:     #6b7280;
  --text-light:     #9ca3af;
  --bg-page:        #f0f9ff;
  --bg-card:        #ffffff;
  --border:         #bae6fd;
  --border-strong:  #7dd3fc;
  --shadow-sm:      0 1px 3px rgba(3,105,161,0.08);
  --shadow-md:      0 4px 12px rgba(3,105,161,0.13);
  --shadow-lg:      0 8px 24px rgba(3,105,161,0.18);
  --radius-sm:      6px;
  --radius-md:      10px;
  --radius-lg:      14px;
  --transition:     all 0.2s ease;
}

/* ─── Reset & Base ─── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; font-size: 16px; }
body {
  font-family: 'PingFang SC', 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg-page);
  color: var(--text-main);
  line-height: 1.7;
  min-height: 100vh;
}

/* ─── Scrollbar ─── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: #f1f5f9; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--accent); }

/* ─── Typography ─── */
h1, h2, h3, h4 { color: var(--primary-dark); line-height: 1.3; }
a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--accent); }

/* ─── Top Navigation ─── */
.top-nav {
  background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary) 100%);
  box-shadow: 0 2px 8px rgba(12,74,110,0.3);
  position: sticky;
  top: 0;
  z-index: 100;
}
.top-nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 1.5rem;
  display: flex;
  align-items: center;
  height: 56px;
  gap: 1rem;
}
.nav-brand {
  font-size: 1.05rem;
  font-weight: 700;
  color: white;
  white-space: nowrap;
  text-decoration: none;
}
.nav-brand:hover { color: #bae6fd; }
.nav-menu {
  display: flex;
  gap: 0.2rem;
  align-items: center;
  flex: 1;
  overflow-x: auto;
  scrollbar-width: none;
}
.nav-menu::-webkit-scrollbar { display: none; }
.nav-group { position: relative; }
.nav-group-btn {
  background: none;
  border: none;
  color: rgba(255,255,255,0.85);
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.85rem;
  white-space: nowrap;
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 0.25rem;
}
.nav-group-btn:hover, .nav-group-btn.active {
  background: rgba(255,255,255,0.15);
  color: white;
}
.nav-dropdown {
  position: absolute;
  top: calc(100% + 6px);
  left: 0;
  background: white;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  min-width: 200px;
  padding: 0.4rem;
  display: none;
  z-index: 200;
  border: 1px solid var(--border);
}
.nav-group:hover .nav-dropdown { display: block; }
.nav-dropdown a {
  display: block;
  padding: 0.5rem 0.85rem;
  border-radius: var(--radius-sm);
  color: var(--text-main);
  font-size: 0.85rem;
  transition: var(--transition);
}
.nav-dropdown a:hover { background: var(--primary-light); color: var(--primary); }
.nav-dropdown a.current { background: var(--primary-light); color: var(--primary); font-weight: 600; }
.nav-hamburger {
  display: none;
  background: none;
  border: none;
  color: white;
  font-size: 1.4rem;
  cursor: pointer;
  padding: 0.3rem;
  margin-left: auto;
}

/* ─── Mobile Nav ─── */
.nav-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.5);
  z-index: 1100;
  backdrop-filter: blur(2px);
  -webkit-backdrop-filter: blur(2px);
}
.nav-overlay.show { display: block; }

.nav-sidebar {
  position: fixed;
  top: 0;
  right: -300px;
  width: 280px;
  height: 100vh;
  background: white;
  z-index: 1200;
  overflow-y: auto;
  transition: right 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  box-shadow: -4px 0 32px rgba(3,105,161,0.2);
}
.nav-sidebar.open { right: 0; }

.sidebar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 20px;
  height: 60px;
  background: linear-gradient(135deg, #0c4a6e, #0369a1);
  color: white;
  font-weight: 600;
  font-size: 0.92rem;
  position: sticky;
  top: 0;
  z-index: 1;
}
.sidebar-close {
  background: none;
  border: none;
  color: rgba(255,255,255,0.8);
  font-size: 1.2rem;
  cursor: pointer;
  padding: 4px 8px;
  line-height: 1;
  transition: color 0.15s;
  border-radius: 4px;
}
.sidebar-close:hover { color: white; background: rgba(255,255,255,0.15); }

.sidebar-body { padding: 8px 0 32px; }

.sidebar-section {
  padding: 12px 20px 4px;
  font-size: 0.7rem;
  font-weight: 700;
  color: #9ca3af;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-top: 4px;
}
.sidebar-link {
  display: block;
  padding: 10px 20px;
  color: var(--text-main);
  text-decoration: none;
  font-size: 0.88rem;
  border-left: 3px solid transparent;
  transition: all 0.15s;
}
.sidebar-link:hover  { background: var(--primary-light); color: var(--primary); border-left-color: #bae6fd; }
.sidebar-link.active { background: #dbeafe; color: var(--primary-dark); border-left-color: var(--primary); font-weight: 600; }

.fab-home {
  position: fixed;
  bottom: 28px;
  right: 24px;
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background: linear-gradient(135deg, #0369a1, #0c4a6e);
  color: white !important;
  text-decoration: none !important;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  box-shadow: 0 4px 16px rgba(3,105,161,0.4);
  z-index: 900;
  transition: transform 0.2s, box-shadow 0.2s;
}
.fab-home:hover { transform: scale(1.1); box-shadow: 0 6px 20px rgba(3,105,161,0.5); }

/* ─── Breadcrumb ─── */
.breadcrumb {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0.75rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.82rem;
  color: var(--text-muted);
}
.breadcrumb a { color: var(--primary); }
.breadcrumb a:hover { color: var(--accent); }

/* ─── Page Hero ─── */
.page-hero {
  background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary) 60%, var(--accent) 100%);
  color: white;
  padding: 2.5rem 1.5rem 2rem;
  text-align: center;
}
.chapter-badge {
  display: inline-block;
  background: rgba(255,255,255,0.15);
  border: 1px solid rgba(255,255,255,0.3);
  border-radius: 20px;
  padding: 0.3rem 1rem;
  font-size: 0.8rem;
  margin-bottom: 0.75rem;
  letter-spacing: 0.03em;
}
.page-hero h1 {
  color: white;
  font-size: clamp(1.6rem, 4vw, 2.4rem);
  margin-bottom: 0.75rem;
  font-weight: 800;
}
.page-hero .subtitle {
  color: rgba(255,255,255,0.85);
  font-size: 1rem;
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.6;
}

/* ─── Main Layout ─── */
.main-content {
  max-width: 1200px;
  margin: 2rem auto;
  padding: 0 1.5rem;
  display: grid;
  grid-template-columns: 1fr 268px;
  gap: 1.5rem;
  align-items: start;
}
.content-body { min-width: 0; }

/* ─── Sidebar ─── */
.sidebar { position: sticky; top: 72px; }
.sidebar-card {
  background: white;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.2rem;
  margin-bottom: 1rem;
}
.sidebar-card-title {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--primary);
  margin-bottom: 0.75rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--primary-light);
}
.sidebar-toc a {
  display: block;
  font-size: 0.82rem;
  color: var(--text-muted);
  padding: 0.3rem 0.6rem;
  border-radius: var(--radius-sm);
  margin-bottom: 0.15rem;
  transition: var(--transition);
}
.sidebar-toc a:hover { background: var(--primary-light); color: var(--primary); }
.sidebar-toc a.active { background: var(--primary-light); color: var(--primary); font-weight: 600; }
.drug-pill {
  display: inline-block;
  background: var(--primary-light);
  color: var(--primary);
  border: 1px solid var(--border-strong);
  border-radius: 20px;
  padding: 0.2rem 0.65rem;
  font-size: 0.73rem;
  font-weight: 600;
  margin: 0.2rem 0.1rem;
}

/* ─── Section Card ─── */
.section-card {
  background: white;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  padding: 1.8rem;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow-sm);
}
.section-card h2 {
  font-size: 1.18rem;
  color: var(--primary-dark);
  margin-bottom: 1.2rem;
  padding-bottom: 0.6rem;
  border-bottom: 2px solid var(--primary-light);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.section-card h3 {
  font-size: 1rem;
  color: var(--primary);
  margin: 1.2rem 0 0.6rem;
}
.section-card p {
  color: var(--text-main);
  margin-bottom: 0.75rem;
  font-size: 0.95rem;
  line-height: 1.75;
}

/* ─── Chapter Intro（承接导读）─── */
.chapter-intro {
  background: linear-gradient(135deg, #f0f9ff, #e0f2fe);
  border: 2px solid var(--border-strong);
  border-left: 5px solid var(--primary);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin-bottom: 1.5rem;
}
.chapter-intro-link {
  font-size: 0.83rem;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
}
.chapter-intro-link a { color: var(--primary); font-weight: 600; }
.chapter-intro h3 { font-size: 1rem; color: var(--primary-dark); margin-bottom: 0.75rem; }
.hook-questions { display: flex; flex-direction: column; gap: 0.5rem; }
.hook-q {
  background: white;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.6rem 0.9rem;
  font-size: 0.88rem;
  color: var(--text-main);
  display: flex;
  gap: 0.5rem;
  align-items: flex-start;
  line-height: 1.55;
}
.hook-q::before {
  content: '?';
  font-weight: 800;
  color: var(--primary);
  flex-shrink: 0;
}
.drug-preview {
  margin-top: 1rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  align-items: center;
  font-size: 0.82rem;
  color: var(--text-muted);
}
.drug-preview-label { font-weight: 600; color: var(--primary); margin-right: 0.2rem; }

/* ─── Four Questions Grid ─── */
.four-questions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin: 1rem 0;
}
.fq-item { background: white; padding: 1.1rem; }
.fq-item:nth-child(odd) { background: #f8fcff; }
.fq-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--primary);
  margin-bottom: 0.4rem;
}
.fq-content { font-size: 0.88rem; color: var(--text-main); line-height: 1.65; }
.fq-content strong { color: var(--primary-dark); }

/* ─── Drug Flow（作用流程图）─── */
.drug-flow {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0;
  margin: 1rem 0;
  padding: 1rem;
  background: #f8fcff;
  border-radius: var(--radius-md);
  border: 1px solid var(--border);
}
.df-step {
  background: white;
  border: 2px solid var(--border-strong);
  border-radius: var(--radius-sm);
  padding: 0.55rem 0.85rem;
  font-size: 0.82rem;
  text-align: center;
  min-width: 88px;
  flex-shrink: 0;
}
.df-step strong { display: block; font-size: 0.76rem; color: var(--primary); margin-bottom: 0.2rem; }
.df-step span { color: var(--text-main); }
.df-step.key { background: var(--primary); border-color: var(--primary); color: white; }
.df-step.key strong { color: rgba(255,255,255,0.8); }
.df-step.key span { color: white; }
.df-step.warn { background: #fef2f2; border-color: #fca5a5; }
.df-step.warn strong { color: #dc2626; }
.df-arrow { color: var(--primary); font-size: 1.3rem; font-weight: 700; padding: 0 0.3rem; flex-shrink: 0; }

/* ─── Drug Compare（药物对比）─── */
.drug-compare {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin: 1rem 0;
}
.dc-col { background: white; padding: 0; }
.dc-header {
  background: var(--primary);
  color: white;
  padding: 0.6rem 1rem;
  font-weight: 700;
  font-size: 0.88rem;
  text-align: center;
}
.dc-header.alt { background: var(--accent); }
.dc-header.dark { background: var(--primary-dark); }
.dc-row {
  display: flex;
  padding: 0.5rem 1rem;
  border-bottom: 1px solid #f3f4f6;
  font-size: 0.83rem;
  gap: 0.5rem;
}
.dc-row:last-child { border-bottom: none; }
.dc-key { font-weight: 600; color: var(--text-muted); min-width: 4.5rem; flex-shrink: 0; font-size: 0.78rem; }
.dc-val { color: var(--text-main); line-height: 1.55; }

/* ─── CS Analogy Box（深蓝色）─── */
.cs-analogy {
  background: linear-gradient(135deg, #0f172a, #1e3a5f);
  color: #e2e8f0;
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin: 1rem 0;
}
.cs-analogy-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #7dd3fc;
  margin-bottom: 0.75rem;
}
.cs-analogy h4 { color: #bae6fd; font-size: 1rem; margin-bottom: 0.75rem; }
.cs-analogy p, .cs-analogy li { font-size: 0.88rem; color: #cbd5e1; line-height: 1.75; margin-bottom: 0.5rem; }
.cs-analogy strong { color: #7dd3fc; }
.cs-analogy code {
  background: rgba(125,211,252,0.15);
  color: #7dd3fc;
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
  font-family: 'Consolas', 'Monaco', monospace;
  font-size: 0.85em;
}
.cs-analogy ul { padding-left: 1.2rem; }

/* ─── Cognitive Expand Box（深绿色）─── */
.cognitive-expand {
  background: linear-gradient(135deg, #064e3b, #065f46);
  color: #d1fae5;
  border-radius: var(--radius-md);
  padding: 1.4rem 1.5rem;
  margin: 1rem 0;
}
.ce-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #6ee7b7;
  margin-bottom: 0.6rem;
}
.ce-title { color: #a7f3d0; font-size: 1rem; font-weight: 700; margin-bottom: 0.5rem; }
.cognitive-expand p, .cognitive-expand li { font-size: 0.88rem; color: #bbf7d0; line-height: 1.75; margin-bottom: 0.4rem; }
.cognitive-expand strong { color: #ecfdf5; }
.cognitive-expand ul { padding-left: 1.2rem; }

/* ─── Clinical Logic Box（蓝色）─── */
.clinical-logic {
  background: linear-gradient(135deg, #0c4a6e, #0369a1);
  color: #e0f2fe;
  border-radius: var(--radius-md);
  padding: 1.3rem 1.5rem;
  margin: 1rem 0;
}
.cl-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #7dd3fc;
  margin-bottom: 0.6rem;
}
.cl-title { color: #bae6fd; font-size: 1rem; font-weight: 700; margin-bottom: 0.5rem; }
.clinical-logic p, .clinical-logic li { font-size: 0.88rem; color: #bae6fd; line-height: 1.75; margin-bottom: 0.4rem; }
.clinical-logic strong { color: white; }
.clinical-logic ul, .clinical-logic ol { padding-left: 1.2rem; }

/* ─── Adverse Box（副作用推导，暗红）─── */
.adverse-box {
  background: linear-gradient(135deg, #450a0a, #7c2d12);
  color: #fee2e2;
  border-radius: var(--radius-md);
  padding: 1.3rem 1.5rem;
  margin: 1rem 0;
}
.ab-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: #fca5a5;
  margin-bottom: 0.6rem;
}
.adverse-box h4 { color: #fecaca; font-size: 1rem; margin-bottom: 0.75rem; }
.adverse-item {
  background: rgba(0,0,0,0.2);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  margin-bottom: 0.6rem;
}
.adverse-item:last-child { margin-bottom: 0; }
.adverse-myth {
  font-size: 0.85rem;
  color: #fca5a5;
  margin-bottom: 0.35rem;
  display: flex;
  gap: 0.4rem;
  align-items: flex-start;
  line-height: 1.55;
}
.adverse-truth {
  font-size: 0.85rem;
  color: #bbf7d0;
  display: flex;
  gap: 0.4rem;
  align-items: flex-start;
  line-height: 1.6;
}
.adverse-myth strong, .adverse-truth strong { color: white; }

/* ─── PK Box（药动学四格）─── */
.pk-box {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin: 1rem 0;
}
.pk-item { background: white; padding: 1.1rem; }
.pk-item:nth-child(odd) { background: #f8fcff; }
.pk-letter {
  font-size: 2rem;
  font-weight: 900;
  color: var(--primary-light);
  -webkit-text-stroke: 2px var(--primary);
  line-height: 1;
  margin-bottom: 0.2rem;
}
.pk-name { font-size: 0.88rem; font-weight: 700; color: var(--primary-dark); margin-bottom: 0.5rem; }
.pk-detail { font-size: 0.82rem; color: var(--text-main); line-height: 1.6; }
.pk-detail strong { color: var(--primary); }

/* ─── Dose Window（治疗窗）─── */
.dose-window {
  background: white;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.2rem;
  margin: 1rem 0;
}
.dw-title { font-size: 0.85rem; font-weight: 700; color: var(--primary-dark); margin-bottom: 0.8rem; text-align: center; }
.dw-bar-container {
  display: flex;
  border-radius: 6px;
  overflow: hidden;
  height: 40px;
  margin-bottom: 0.5rem;
}
.dw-zone-low { background: #9ca3af; flex: 2; display: flex; align-items: center; justify-content: center; color: white; font-size: 0.72rem; font-weight: 600; }
.dw-zone-therapeutic { background: var(--primary); flex: 3; display: flex; align-items: center; justify-content: center; color: white; font-size: 0.72rem; font-weight: 700; }
.dw-zone-toxic { background: #dc2626; flex: 2; display: flex; align-items: center; justify-content: center; color: white; font-size: 0.72rem; font-weight: 600; }
.dw-labels { display: flex; justify-content: space-between; font-size: 0.72rem; color: var(--text-muted); padding: 0 0.2rem; }
.dw-info { margin-top: 0.75rem; display: flex; gap: 1rem; flex-wrap: wrap; }
.dw-info-item { display: flex; align-items: center; gap: 0.3rem; font-size: 0.8rem; color: var(--text-main); }
.dw-dot { width: 10px; height: 10px; border-radius: 50%; flex-shrink: 0; }
.dw-dot.narrow { background: #dc2626; }
.dw-dot.wide { background: #16a34a; }
.dw-dot.medium { background: var(--primary); }

/* ─── Receptor Badge ─── */
.receptor-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.25rem 0.6rem;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 700;
  margin: 0.15rem;
}
.rb-gpcr  { background: #dbeafe; color: #1d4ed8; border: 1px solid #93c5fd; }
.rb-ion   { background: #d1fae5; color: #065f46; border: 1px solid #6ee7b7; }
.rb-enzyme{ background: #fef3c7; color: #92400e; border: 1px solid #fcd34d; }
.rb-nuclear{ background: #ede9fe; color: #5b21b6; border: 1px solid #c4b5fd; }

/* ─── Drug Network（药物关联网）─── */
.drug-network {
  background: #f8fcff;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.2rem;
  margin: 1rem 0;
}
.dn-title {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--primary);
  margin-bottom: 0.75rem;
}
.dn-items { display: flex; flex-wrap: wrap; gap: 0.6rem; }
.dn-item {
  display: flex;
  align-items: center;
  gap: 0.3rem;
  background: white;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.4rem 0.75rem;
  font-size: 0.82rem;
  color: var(--text-main);
}
.dn-from { font-weight: 700; color: var(--primary); font-size: 0.78rem; }
.dn-arrow { color: var(--accent); font-weight: 700; }
.dn-to a { color: var(--primary); font-weight: 600; }
.dn-to a:hover { color: var(--accent); }

/* ─── Info / Warning Boxes ─── */
.info-box {
  background: var(--primary-light);
  border: 1px solid var(--border-strong);
  border-left: 4px solid var(--primary);
  border-radius: var(--radius-sm);
  padding: 0.9rem 1.1rem;
  margin: 0.75rem 0;
  font-size: 0.88rem;
  color: var(--text-main);
  line-height: 1.65;
}
.info-box strong { color: var(--primary-dark); }
.warning-box {
  background: #fff7ed;
  border: 1px solid #fdba74;
  border-left: 4px solid #ea580c;
  border-radius: var(--radius-sm);
  padding: 0.9rem 1.1rem;
  margin: 0.75rem 0;
  font-size: 0.88rem;
  color: #7c2d12;
  line-height: 1.65;
}
.warning-box strong { color: #c2410c; }

/* ─── Chapter Nav Buttons ─── */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin: 2rem 0 1rem;
  gap: 1rem;
  flex-wrap: wrap;
}
.chapter-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.65rem 1.2rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 600;
  transition: var(--transition);
  text-decoration: none;
}
.chapter-nav-btn.prev { background: white; border: 2px solid var(--border-strong); color: var(--primary); }
.chapter-nav-btn.prev:hover { background: var(--primary-light); }
.chapter-nav-btn.next { background: var(--primary); color: white; border: 2px solid var(--primary); }
.chapter-nav-btn.next:hover { background: var(--primary-dark); border-color: var(--primary-dark); }

/* ─── Index Page ─── */
.hero-index {
  background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary) 50%, var(--accent) 100%);
  color: white;
  padding: 3.5rem 1.5rem 3rem;
  text-align: center;
}
.hero-index h1 { color: white; font-size: clamp(2rem, 5vw, 3rem); font-weight: 800; margin-bottom: 0.75rem; }
.hero-index .tagline { color: rgba(255,255,255,0.9); font-size: 1.05rem; max-width: 640px; margin: 0 auto 1.5rem; line-height: 1.65; }
.hero-index .tagline strong { color: white; }
.hero-stats { display: flex; justify-content: center; gap: 2.5rem; flex-wrap: wrap; margin-top: 1.5rem; }
.hero-stat-num { font-size: 2.2rem; font-weight: 800; color: white; line-height: 1; }
.hero-stat-label { font-size: 0.8rem; color: rgba(255,255,255,0.75); margin-top: 0.2rem; }
.index-content { max-width: 1100px; margin: 2rem auto; padding: 0 1.5rem; }
.philosophy-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.2rem;
  margin-bottom: 2.5rem;
}
.philosophy-card {
  background: white;
  border: 1px solid var(--border);
  border-top: 4px solid var(--primary);
  border-radius: var(--radius-md);
  padding: 1.3rem;
  text-align: center;
}
.philosophy-icon { font-size: 2rem; margin-bottom: 0.5rem; }
.philosophy-title { font-size: 1rem; font-weight: 700; color: var(--primary-dark); margin-bottom: 0.4rem; }
.philosophy-desc { font-size: 0.83rem; color: var(--text-muted); line-height: 1.6; }
.chapter-group { margin-bottom: 2.5rem; }
.chapter-group-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--primary-dark);
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding-bottom: 0.4rem;
  border-bottom: 2px solid var(--primary-light);
}
.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 1rem;
}
.chapter-card {
  background: white;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.2rem;
  transition: var(--transition);
  text-decoration: none;
  display: block;
}
.chapter-card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); border-color: var(--border-strong); }
.chapter-card-num { font-size: 0.72rem; font-weight: 700; color: var(--primary); text-transform: uppercase; letter-spacing: 0.05em; margin-bottom: 0.35rem; }
.chapter-card-title { font-size: 1rem; font-weight: 700; color: var(--text-main); margin-bottom: 0.4rem; line-height: 1.3; }
.chapter-card-desc { font-size: 0.8rem; color: var(--text-muted); line-height: 1.5; }
.chapter-card-drugs { margin-top: 0.6rem; display: flex; flex-wrap: wrap; gap: 0.3rem; }
.drug-tag-mini {
  font-size: 0.7rem;
  background: var(--primary-light);
  color: var(--primary);
  padding: 0.1rem 0.45rem;
  border-radius: 10px;
  border: 1px solid var(--border);
}
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.2rem;
  margin-bottom: 2rem;
}
.tool-card {
  background: linear-gradient(135deg, var(--primary-dark), var(--primary));
  color: white;
  border-radius: var(--radius-md);
  padding: 1.3rem;
  text-decoration: none;
  transition: var(--transition);
}
.tool-card:hover { transform: translateY(-2px); box-shadow: var(--shadow-lg); }
.tool-card-icon { font-size: 2rem; margin-bottom: 0.5rem; }
.tool-card-title { font-size: 1rem; font-weight: 700; color: white; margin-bottom: 0.3rem; }
.tool-card-desc { font-size: 0.82rem; color: rgba(255,255,255,0.8); line-height: 1.5; }

/* ─── Footer ─── */
.site-footer {
  background: var(--primary-dark);
  color: rgba(255,255,255,0.7);
  text-align: center;
  padding: 2rem 1.5rem;
  margin-top: 3rem;
  font-size: 0.85rem;
}

/* ─── Responsive ─── */
@media (max-width: 900px) {
  .main-content { grid-template-columns: 1fr; }
  .sidebar { position: static; }
  .four-questions, .drug-compare, .pk-box { grid-template-columns: 1fr; }
}
@media (max-width: 640px) {
  .page-hero { padding: 1.8rem 1rem 1.5rem; }
  .main-content { padding: 0 1rem; margin: 1rem auto; }
  .section-card { padding: 1.2rem 1rem; }
  .nav-menu { display: none; }
  .nav-hamburger { display: block; }
  .drug-flow { flex-direction: column; align-items: flex-start; }
  .df-arrow { transform: rotate(90deg); align-self: center; }
  .chapter-nav { flex-direction: column; }
  .chapter-nav-btn { width: 100%; justify-content: center; }
  .hero-stats { gap: 1.5rem; }
  .hero-index { padding: 2.5rem 1rem 2rem; }
}