/* ===== Reset & Variables ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #f4f4f9;
  --text: #1a1a2e;
  --primary: #0f3460;
  --accent: #e94560;
  --card-bg: rgba(255,255,255,0.75);
  --shadow: 0 4px 20px rgba(0,0,0,0.08);
  --radius: 16px;
  --max-width: 1200px;
  --glass-border: rgba(255,255,255,0.25);
  --glass-blur: blur(12px);
  --transition: 0.3s ease;
}
[data-theme="dark"] {
  --bg: #121212;
  --text: #e0e0e0;
  --primary: #1a1a2e;
  --accent: #ff6b6b;
  --card-bg: rgba(30,30,50,0.8);
  --shadow: 0 4px 20px rgba(0,0,0,0.5);
}
body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background var(--transition), color var(--transition);
}

/* ===== Container ===== */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 20px;
}

/* ===== Header ===== */
header {
  background: var(--primary);
  color: #fff;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 2px 10px rgba(0,0,0,0.2);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
}
.header-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 0;
}
.logo {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: 1px;
}
.logo span { color: var(--accent); }
nav ul {
  list-style: none;
  display: flex;
  gap: 24px;
}
nav a {
  color: #fff;
  text-decoration: none;
  font-weight: 500;
  font-size: 0.95rem;
  transition: opacity 0.2s, transform 0.2s;
  position: relative;
}
nav a::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--accent);
  transition: width 0.3s;
}
nav a:hover { opacity: 0.8; transform: translateY(-2px); }
nav a:hover::after { width: 100%; }
.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  color: #fff;
  font-size: 1.8rem;
  cursor: pointer;
}

/* ===== Hero Section (渐变Banner) ===== */
.hero {
  background: linear-gradient(135deg, var(--primary) 0%, #16213e 100%);
  color: #fff;
  padding: 80px 0 60px;
  text-align: center;
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 70%, rgba(233,69,96,0.15) 0%, transparent 50%),
              radial-gradient(circle at 70% 30%, rgba(15,52,96,0.2) 0%, transparent 50%);
  animation: heroGlow 8s infinite alternate;
  pointer-events: none;
}
@keyframes heroGlow {
  0% { transform: translate(0,0) scale(1); }
  100% { transform: translate(10%,10%) scale(1.1); }
}
.hero h1 {
  font-size: 2.8rem;
  margin-bottom: 16px;
  font-weight: 800;
  position: relative;
  z-index: 1;
  animation: fadeInUp 0.8s ease;
}
.hero p {
  font-size: 1.2rem;
  max-width: 700px;
  margin: 0 auto 32px;
  opacity: 0.9;
  position: relative;
  z-index: 1;
  animation: fadeInUp 0.8s ease 0.2s both;
}
.hero-buttons {
  display: flex;
  justify-content: center;
  gap: 16px;
  flex-wrap: wrap;
  position: relative;
  z-index: 1;
  animation: fadeInUp 0.8s ease 0.4s both;
}
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ===== Buttons ===== */
.btn {
  display: inline-block;
  padding: 14px 36px;
  border-radius: 50px;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.3s;
  font-size: 1rem;
  cursor: pointer;
  border: none;
}
.btn-primary {
  background: var(--accent);
  color: #fff;
  box-shadow: 0 4px 14px rgba(233,69,96,0.3);
}
.btn-primary:hover {
  transform: translateY(-2px) scale(1.02);
  box-shadow: 0 8px 24px rgba(233,69,96,0.5);
}
.btn-outline {
  background: transparent;
  color: #fff;
  border: 2px solid #fff;
  backdrop-filter: blur(4px);
}
.btn-outline:hover {
  background: rgba(255,255,255,0.15);
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgba(255,255,255,0.2);
}

/* ===== Sections ===== */
section { padding: 60px 0; }
.section-title {
  font-size: 2rem;
  text-align: center;
  margin-bottom: 40px;
  font-weight: 700;
  color: var(--primary);
  position: relative;
  display: inline-block;
  left: 50%;
  transform: translateX(-50%);
}
.section-title::after {
  content: '';
  display: block;
  width: 60px;
  height: 4px;
  background: var(--accent);
  margin: 10px auto 0;
  border-radius: 2px;
}

/* ===== Card Grid & Cards (圆角卡片 + 毛玻璃) ===== */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}
.card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow);
  transition: transform 0.3s, box-shadow 0.3s, background 0.3s;
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  position: relative;
  overflow: hidden;
}
.card::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 30% 30%, rgba(233,69,96,0.05), transparent 60%);
  opacity: 0;
  transition: opacity 0.5s;
}
.card:hover::before { opacity: 1; }
.card:hover {
  transform: translateY(-6px) scale(1.01);
  box-shadow: 0 12px 40px rgba(0,0,0,0.15);
}
.card h3 {
  color: var(--primary);
  margin-bottom: 12px;
  font-size: 1.2rem;
}
.card p { color: var(--text); }

/* ===== About ===== */
.about-content {
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
}
.about-content p { margin-bottom: 16px; }

/* ===== Stats (渐变背景) ===== */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 20px;
  text-align: center;
}
.stat-item {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  transition: transform 0.3s, box-shadow 0.3s;
}
.stat-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 30px rgba(0,0,0,0.2);
}
.stat-number {
  font-size: 2.4rem;
  font-weight: 800;
  color: var(--accent);
}
.stat-label { color: #666; margin-top: 8px; }

/* ===== FAQ ===== */
.faq-item {
  background: var(--card-bg);
  border-radius: var(--radius);
  margin-bottom: 12px;
  box-shadow: var(--shadow);
  overflow: hidden;
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  transition: box-shadow 0.3s;
}
.faq-item:hover { box-shadow: 0 6px 24px rgba(0,0,0,0.12); }
.faq-question {
  padding: 20px 24px;
  cursor: pointer;
  font-weight: 600;
  display: flex;
  justify-content: space-between;
  align-items: center;
  transition: background 0.2s;
}
.faq-question:hover { background: rgba(233,69,96,0.05); }
.faq-question::after {
  content: '+';
  font-size: 1.4rem;
  transition: transform 0.3s;
  color: var(--accent);
}
.faq-item.active .faq-question::after { transform: rotate(45deg); }
.faq-answer {
  padding: 0 24px 20px;
  display: none;
  color: var(--text);
}
.faq-item.active .faq-answer { display: block; animation: fadeIn 0.3s ease; }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

/* ===== HowTo Steps ===== */
.howto-steps {
  counter-reset: step;
  max-width: 700px;
  margin: 0 auto;
}
.howto-step {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 20px 24px 20px 60px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
  position: relative;
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  transition: transform 0.3s, box-shadow 0.3s;
}
.howto-step:hover {
  transform: translateX(4px);
  box-shadow: 0 6px 24px rgba(0,0,0,0.12);
}
.howto-step::before {
  counter-increment: step;
  content: counter(step);
  position: absolute;
  left: 16px;
  top: 20px;
  background: var(--accent);
  color: #fff;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  box-shadow: 0 2px 8px rgba(233,69,96,0.3);
}

/* ===== Article Grid ===== */
.article-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}
.article-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  backdrop-filter: var(--glass-blur);
  -webkit-backdrop-filter: var(--glass-blur);
  border: 1px solid var(--glass-border);
  transition: transform 0.3s, box-shadow 0.3s;
}
.article-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 30px rgba(0,0,0,0.12);
}
.article-card h3 { color: var(--primary); margin-bottom: 8px; }
.article-card .meta { font-size: 0.85rem; color: #888; margin-bottom: 12px; }
.article-card a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.2s;
}
.article-card a:hover { color: #c0392b; text-decoration: underline; }

/* ===== Contact ===== */
.contact-info { text-align: center; }
.contact-info p { margin-bottom: 8px; }

/* ===== Footer ===== */
footer {
  background: var(--primary);
  color: #fff;
  padding: 40px 0 20px;
}
.footer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 24px;
  margin-bottom: 24px;
}
.footer-grid h4 { margin-bottom: 12px; font-size: 1.1rem; }
.footer-grid a {
  color: rgba(255,255,255,0.8);
  text-decoration: none;
  display: block;
  margin-bottom: 6px;
  font-size: 0.9rem;
  transition: color 0.2s, transform 0.2s;
}
.footer-grid a:hover { color: #fff; transform: translateX(4px); }
.footer-bottom {
  border-top: 1px solid rgba(255,255,255,0.2);
  padding-top: 20px;
  text-align: center;
  font-size: 0.85rem;
  opacity: 0.7;
}

/* ===== Back to Top ===== */
.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  background: var(--accent);
  color: #fff;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  cursor: pointer;
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
  border: none;
  z-index: 99;
  transition: opacity 0.3s, transform 0.3s;
  opacity: 0;
  visibility: hidden;
  backdrop-filter: blur(4px);
}
.back-to-top.visible { opacity: 1; visibility: visible; }
.back-to-top:hover {
  transform: scale(1.1) translateY(-2px);
  box-shadow: 0 6px 20px rgba(233,69,96,0.5);
}

/* ===== Scroll Animations (via class added by IntersectionObserver) ===== */
.scroll-animate {
  opacity: 0;
  transform: translateY(40px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}
.scroll-animate.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .hero h1 { font-size: 2rem; }
  .hero p { font-size: 1rem; }
  nav ul {
    display: none;
    flex-direction: column;
    background: var(--primary);
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    padding: 20px;
    gap: 12px;
    backdrop-filter: var(--glass-blur);
    -webkit-backdrop-filter: var(--glass-blur);
  }
  nav ul.open { display: flex; }
  .mobile-menu-btn { display: block; }
  .section-title { font-size: 1.6rem; }
  .card-grid { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: 1fr 1fr; }
  .article-grid { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .back-to-top { bottom: 20px; right: 20px; width: 40px; height: 40px; font-size: 1.2rem; }
}

/* ===== Dark Mode Support ===== */
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #121212;
    --text: #e0e0e0;
    --primary: #1a1a2e;
    --accent: #ff6b6b;
    --card-bg: rgba(30,30,50,0.8);
    --shadow: 0 4px 20px rgba(0,0,0,0.5);
  }
}

/* ===== Additional Polish ===== */
::selection { background: var(--accent); color: #fff; }
html { scroll-behavior: smooth; }

/* ===== Glass effect for stat section inside gradient ===== */
#stats .stat-item {
  background: rgba(255,255,255,0.12);
  border: 1px solid rgba(255,255,255,0.2);
  color: #fff;
}
#stats .stat-label { color: rgba(255,255,255,0.8); }
#stats .stat-number { color: var(--accent); }

/* ===== Button hover scale for all ===== */
.btn:active { transform: scale(0.98); }

/* ===== Smooth scroll offset for sticky header ===== */
section[id] {
  scroll-margin-top: 80px;
}