/* ==========================================
   天年 · TianNian — 黄帝内经的人口智慧
   Huangdi Neijing's Wisdom on Population
   ========================================== */

/* --- CSS Variables (Theme) --- */
:root {
  --color-primary: #8B4513;        /* 檀木棕 */
  --color-primary-light: #A0522D;  /* 赭石 */
  --color-secondary: #D4A574;      /* 麦芽金 */
  --color-accent: #C41E3A;         /* 朱砂红 */
  --color-accent-light: #E8A0A0;
  --color-bg: #FFFBF5;             /* 宣纸白 */
  --color-bg-alt: #F5EDE0;         /* 旧纸黄 */
  --color-bg-dark: #2C1810;        /* 墨黑褐 */
  --color-text: #3C2415;           /* 墨色 */
  --color-text-light: #7A5C40;
  --color-text-muted: #A08060;
  --color-border: #D4C5A9;
  --font-cn: 'Noto Serif SC', 'STSong', 'SimSun', '宋体', serif;
  --font-en: 'Noto Serif', 'Georgia', serif;
  --font-sans: 'Noto Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --shadow-sm: 0 1px 3px rgba(44, 24, 16, 0.08);
  --shadow-md: 0 4px 12px rgba(44, 24, 16, 0.12);
  --shadow-lg: 0 8px 30px rgba(44, 24, 16, 0.15);
  --radius: 8px;
  --radius-lg: 16px;
  --transition: all 0.3s ease;
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-cn);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.8;
  overflow-x: hidden;
}

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: var(--transition);
}
a:hover { color: var(--color-accent); }

img { max-width: 100%; height: auto; }

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

/* --- Language Visibility --- */
.lang-zh { display: block; }
.lang-en { display: none; }

body.lang-en .lang-zh { display: none; }
body.lang-en .lang-en { display: block; }

/* --- Typography --- */
h1, h2, h3, h4 {
  font-weight: 700;
  line-height: 1.3;
}

.section-title {
  text-align: center;
  font-size: 2rem;
  margin-bottom: 0.5rem;
  color: var(--color-primary);
}

.section-subtitle {
  text-align: center;
  font-size: 0.95rem;
  color: var(--color-text-muted);
  margin-bottom: 2.5rem;
  font-family: var(--font-sans);
}

.section-divider {
  width: 60px;
  height: 3px;
  background: var(--color-secondary);
  margin: 0 auto 1.5rem;
  border-radius: 2px;
}

/* --- Header / Navigation --- */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255, 251, 245, 0.95);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-border);
  transition: var(--transition);
}

.header.scrolled {
  box-shadow: var(--shadow-md);
}

.header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 70px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--color-primary);
}

.logo-icon {
  width: 36px;
  height: 36px;
  background: var(--color-primary);
  color: var(--color-bg);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  font-family: var(--font-cn);
  line-height: 1;
}

.nav-menu {
  display: flex;
  list-style: none;
  gap: 1.5rem;
  align-items: center;
}

.nav-menu a {
  font-size: 0.9rem;
  color: var(--color-text-light);
  padding: 0.3rem 0;
  position: relative;
  font-family: var(--font-sans);
}

.nav-menu a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--color-accent);
  transition: var(--transition);
}

.nav-menu a:hover::after,
.nav-menu a.active::after {
  width: 100%;
}

.lang-toggle {
  display: flex;
  align-items: center;
  gap: 4px;
  padding: 6px 14px;
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
  color: var(--color-text-light);
  transition: var(--transition);
  font-family: var(--font-sans);
}

.lang-toggle:hover {
  background: var(--color-secondary);
  color: var(--color-bg);
  border-color: var(--color-secondary);
}

.mobile-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 5px;
}

.mobile-toggle span {
  width: 24px;
  height: 2px;
  background: var(--color-text);
  transition: var(--transition);
  border-radius: 2px;
}

/* --- Hero Section --- */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 100px 20px 60px;
  background: linear-gradient(135deg, var(--color-bg) 0%, var(--color-bg-alt) 50%, #E8D5C0 100%);
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 50%, rgba(139, 69, 19, 0.03) 0%, transparent 50%),
              radial-gradient(circle at 70% 50%, rgba(196, 30, 58, 0.02) 0%, transparent 50%);
  animation: heroGlow 20s ease-in-out infinite alternate;
}

@keyframes heroGlow {
  0% { transform: translate(0, 0); }
  100% { transform: translate(-5%, -5%); }
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 800px;
}

.hero-badge {
  display: inline-block;
  padding: 6px 18px;
  background: rgba(196, 30, 58, 0.1);
  color: var(--color-accent);
  border-radius: 20px;
  font-size: 0.85rem;
  font-family: var(--font-sans);
  margin-bottom: 1.5rem;
  letter-spacing: 2px;
}

.hero-title {
  font-size: 4rem;
  font-weight: 900;
  color: var(--color-primary);
  margin-bottom: 0.5rem;
  letter-spacing: 8px;
}

.hero-title-en {
  font-family: var(--font-en);
  font-size: 2rem;
  font-weight: 400;
  color: var(--color-text-muted);
  margin-bottom: 1.5rem;
  letter-spacing: 4px;
  font-style: italic;
}

.hero-subtitle {
  font-size: 1.2rem;
  color: var(--color-text-light);
  margin-bottom: 0.8rem;
  font-family: var(--font-sans);
  line-height: 1.6;
}

.hero-desc {
  font-size: 1rem;
  color: var(--color-text-muted);
  margin-bottom: 2rem;
  font-family: var(--font-sans);
  line-height: 1.8;
  max-width: 650px;
  margin-left: auto;
  margin-right: auto;
}

.hero-quote {
  font-size: 1.1rem;
  font-style: italic;
  color: var(--color-primary-light);
  border-left: 3px solid var(--color-secondary);
  padding: 1rem 1.5rem;
  margin: 1.5rem auto;
  max-width: 550px;
  text-align: left;
  background: rgba(255,255,255,0.5);
  border-radius: 0 var(--radius) var(--radius) 0;
}

.hero-quote .source {
  display: block;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin-top: 0.5rem;
  font-style: normal;
}

.btn-group {
  display: flex;
  gap: 1rem;
  justify-content: center;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 12px 32px;
  border-radius: 30px;
  font-size: 0.95rem;
  font-family: var(--font-sans);
  font-weight: 500;
  cursor: pointer;
  transition: var(--transition);
  border: none;
}

.btn-primary {
  background: var(--color-primary);
  color: var(--color-bg);
}

.btn-primary:hover {
  background: var(--color-primary-light);
  color: var(--color-bg);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.btn-outline {
  background: transparent;
  color: var(--color-primary);
  border: 2px solid var(--color-primary);
}

.btn-outline:hover {
  background: var(--color-primary);
  color: var(--color-bg);
  transform: translateY(-2px);
}

.scroll-indicator {
  position: absolute;
  bottom: 30px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  color: var(--color-text-muted);
  font-size: 0.8rem;
  font-family: var(--font-sans);
  animation: bounce 2s infinite;
}

@keyframes bounce {
  0%, 100% { transform: translateX(-50%) translateY(0); }
  50% { transform: translateX(-50%) translateY(10px); }
}

.scroll-indicator .arrow {
  width: 20px;
  height: 20px;
  border-right: 2px solid var(--color-text-muted);
  border-bottom: 2px solid var(--color-text-muted);
  transform: rotate(45deg);
}

/* --- Section Common --- */
.section {
  padding: 80px 0;
}

.section-alt {
  background: var(--color-bg-alt);
}

/* --- Stats / 人口现状 --- */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 24px;
  margin-top: 2rem;
}

.stat-card {
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  padding: 2rem 1.5rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: var(--transition);
}

.stat-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.stat-number {
  font-size: 2.8rem;
  font-weight: 900;
  color: var(--color-accent);
  line-height: 1.2;
  margin-bottom: 0.5rem;
}

.stat-number .unit {
  font-size: 1rem;
  font-weight: 400;
  color: var(--color-text-muted);
}

.stat-label {
  font-size: 0.95rem;
  color: var(--color-text-light);
  font-family: var(--font-sans);
}

.stat-trend {
  display: inline-block;
  margin-top: 0.5rem;
  font-size: 0.85rem;
  padding: 2px 10px;
  border-radius: 12px;
  font-family: var(--font-sans);
}

.stat-trend.down { background: rgba(196, 30, 58, 0.1); color: var(--color-accent); }
.stat-trend.up { background: rgba(139, 69, 19, 0.1); color: var(--color-primary); }

/* --- Wisdom / 内经智慧 --- */
.wisdom-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 30px;
}

.wisdom-card {
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: var(--transition);
}

.wisdom-card:hover {
  box-shadow: var(--shadow-md);
}

.wisdom-card .classic-text {
  font-size: 1.1rem;
  color: var(--color-primary);
  line-height: 2;
  margin-bottom: 1rem;
  padding: 1rem;
  background: var(--color-bg-alt);
  border-radius: var(--radius);
}

.wisdom-card .translation {
  font-size: 0.95rem;
  color: var(--color-text-light);
  font-family: var(--font-sans);
  line-height: 1.8;
}

.wisdom-card h3 {
  color: var(--color-primary);
  margin-bottom: 1rem;
  font-size: 1.2rem;
}

/* --- Timeline / 人口趋势 --- */
.timeline {
  position: relative;
  max-width: 800px;
  margin: 0 auto;
  padding: 20px 0;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  width: 2px;
  height: 100%;
  background: var(--color-border);
  top: 0;
}

.timeline-item {
  display: flex;
  justify-content: flex-start;
  align-items: flex-start;
  margin-bottom: 2rem;
  position: relative;
}

.timeline-item:nth-child(even) {
  flex-direction: row-reverse;
}

.timeline-content {
  width: 45%;
  padding: 1.5rem;
  background: var(--color-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
}

.timeline-year {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-accent);
  margin-bottom: 0.5rem;
}

.timeline-dot {
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  width: 12px;
  height: 12px;
  background: var(--color-secondary);
  border: 3px solid var(--color-bg);
  border-radius: 50%;
  top: 1.8rem;
  z-index: 1;
}

/* --- Health Tips / 养生备孕 --- */
.tips-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}

.tip-card {
  background: var(--color-bg);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: var(--transition);
  position: relative;
  overflow: hidden;
}

.tip-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background: var(--color-secondary);
}

.tip-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.tip-icon {
  font-size: 2rem;
  margin-bottom: 1rem;
}

.tip-card h3 {
  font-size: 1.1rem;
  color: var(--color-primary);
  margin-bottom: 0.8rem;
}

.tip-card p {
  font-size: 0.92rem;
  color: var(--color-text-light);
  font-family: var(--font-sans);
  line-height: 1.7;
}

/* --- FAQ / 知识问答 --- */
.faq-list {
  max-width: 800px;
  margin: 0 auto;
}

.faq-item {
  background: var(--color-bg);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  margin-bottom: 12px;
  overflow: hidden;
  transition: var(--transition);
}

.faq-item:hover {
  border-color: var(--color-secondary);
}

.faq-question {
  padding: 1.2rem 1.5rem;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-weight: 600;
  color: var(--color-text);
  font-size: 1rem;
  background: none;
  border: none;
  width: 100%;
  text-align: left;
  font-family: var(--font-cn);
}

.faq-question .icon {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-secondary);
  font-size: 1.2rem;
}

.faq-item.active .faq-question .icon {
  transform: rotate(45deg);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, padding 0.3s ease;
  padding: 0 1.5rem;
  color: var(--color-text-light);
  font-family: var(--font-sans);
  font-size: 0.93rem;
  line-height: 1.8;
}

.faq-item.active .faq-answer {
  max-height: 500px;
  padding: 0 1.5rem 1.2rem;
}

/* --- About Section --- */
.about-content {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
  align-items: center;
}

.about-text {
  font-family: var(--font-sans);
  line-height: 2;
  color: var(--color-text-light);
}

.about-text p {
  margin-bottom: 1rem;
}

.about-vision {
  background: var(--color-bg);
  padding: 2rem;
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
}

.about-vision h3 {
  color: var(--color-primary);
  margin-bottom: 1rem;
  font-size: 1.2rem;
}

.about-vision ul {
  list-style: none;
  padding: 0;
}

.about-vision li {
  padding: 0.6rem 0;
  border-bottom: 1px solid var(--color-border);
  font-family: var(--font-sans);
  color: var(--color-text-light);
  display: flex;
  align-items: flex-start;
  gap: 10px;
}

.about-vision li:last-child { border-bottom: none; }

.about-vision li::before {
  content: '✦';
  color: var(--color-secondary);
  flex-shrink: 0;
}

/* --- Footer --- */
.footer {
  background: var(--color-bg-dark);
  color: var(--color-bg);
  padding: 40px 0 20px;
}

.footer-content {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: 40px;
  margin-bottom: 30px;
}

.footer-brand .logo {
  color: var(--color-bg);
  margin-bottom: 1rem;
}

.footer-brand p {
  font-size: 0.9rem;
  color: rgba(255, 251, 245, 0.7);
  font-family: var(--font-sans);
  line-height: 1.8;
}

.footer h4 {
  color: var(--color-secondary);
  margin-bottom: 1rem;
  font-size: 1rem;
}

.footer ul {
  list-style: none;
}

.footer ul li {
  margin-bottom: 0.5rem;
}

.footer ul a {
  color: rgba(255, 251, 245, 0.7);
  font-size: 0.9rem;
  font-family: var(--font-sans);
}

.footer ul a:hover {
  color: var(--color-secondary);
}

.footer-bottom {
  border-top: 1px solid rgba(255, 251, 245, 0.1);
  padding-top: 20px;
  text-align: center;
  font-size: 0.85rem;
  color: rgba(255, 251, 245, 0.5);
  font-family: var(--font-sans);
}

/* --- Responsive --- */
@media (max-width: 768px) {
  .mobile-toggle {
    display: flex;
  }

  .nav-menu {
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    background: var(--color-bg);
    flex-direction: column;
    padding: 20px;
    gap: 1rem;
    box-shadow: var(--shadow-md);
    transform: translateY(-100%);
    opacity: 0;
    transition: var(--transition);
    pointer-events: none;
    border-bottom: 1px solid var(--color-border);
  }

  .nav-menu.open {
    transform: translateY(0);
    opacity: 1;
    pointer-events: all;
  }

  .hero-title {
    font-size: 2.5rem;
    letter-spacing: 4px;
  }

  .hero-title-en {
    font-size: 1.4rem;
  }

  .section-title {
    font-size: 1.6rem;
  }

  .stats-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .wisdom-grid {
    grid-template-columns: 1fr;
  }

  .timeline::before { left: 20px; }
  .timeline-item,
  .timeline-item:nth-child(even) {
    flex-direction: row;
    padding-left: 40px;
  }
  .timeline-content { width: 100%; }
  .timeline-dot { left: 20px; }

  .about-content {
    grid-template-columns: 1fr;
  }

  .footer-content {
    grid-template-columns: 1fr;
    gap: 30px;
  }
}

@media (max-width: 480px) {
  .stats-grid {
    grid-template-columns: 1fr;
  }

  .btn-group {
    flex-direction: column;
    align-items: center;
  }

  .hero-title {
    font-size: 2rem;
  }
}

/* --- Animations --- */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Language switch safety: when English mode is active, English .fade-in
   elements must be fully opaque — the entrance animation only plays on
   initial page load, not on language toggles. This rule has higher
   specificity than .fade-in { opacity:0 } and uses !important to
   guarantee it overrides both .fade-in and .fade-in.visible rules. */
body.lang-en .lang-en.fade-in {
  opacity: 1 !important;
  transform: translateY(0) !important;
}