/* style.css - B体育官方网站完整样式 */
:root {
  --primary: #1a1a2e;
  --accent: #ffd700;
  --bg: #f8f9fa;
  --bg-card: #ffffff;
  --text: #222222;
  --text-secondary: #555555;
  --border: #e0e0e0;
  --shadow: rgba(0, 0, 0, 0.06);
  --shadow-hover: rgba(0, 0, 0, 0.12);
  --nav-bg: rgba(255, 255, 255, 0.85);
  --hero-start: #1a1a2e;
  --hero-end: #16213e;
  --footer-bg: #1a1a2e;
  --gradient-overlay: rgba(26, 26, 46, 0.6);
  --glass-bg: rgba(255, 255, 255, 0.15);
  --glass-border: rgba(255, 255, 255, 0.25);
  --glass-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
  --transition: 0.3s ease;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

body.dark {
  --bg: #121212;
  --bg-card: #1e1e1e;
  --text: #e0e0e0;
  --text-secondary: #bbbbbb;
  --border: #333333;
  --shadow: rgba(0, 0, 0, 0.4);
  --shadow-hover: rgba(0, 0, 0, 0.6);
  --nav-bg: rgba(30, 30, 30, 0.85);
  --hero-start: #0d1117;
  --hero-end: #0d1117;
  --footer-bg: #0d1117;
  --glass-bg: rgba(30, 30, 30, 0.2);
  --glass-border: rgba(255, 255, 255, 0.1);
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  transition: background var(--transition), color var(--transition);
  overflow-x: hidden;
}

a {
  color: #1a73e8;
  text-decoration: none;
  transition: color var(--transition);
}

a:hover {
  text-decoration: underline;
  color: var(--accent);
}

/* Navigation */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  padding: 12px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  transition: background var(--transition), border-color var(--transition);
  box-shadow: 0 2px 20px rgba(0, 0, 0, 0.05);
}

.nav .logo {
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--primary);
  transition: color var(--transition);
  letter-spacing: 1px;
}

body.dark .nav .logo {
  color: var(--accent);
}

.nav .links {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

.nav a {
  color: var(--text);
  margin: 0 6px;
  font-size: 0.95rem;
  padding: 6px 12px;
  border-radius: 20px;
  transition: background var(--transition), color var(--transition);
}

.nav a:hover {
  background: rgba(255, 215, 0, 0.15);
  color: var(--primary);
  text-decoration: none;
}

body.dark .nav a:hover {
  background: rgba(255, 215, 0, 0.2);
  color: var(--accent);
}

.nav .btn-theme {
  background: none;
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 6px 16px;
  cursor: pointer;
  font-size: 0.85rem;
  color: var(--text);
  transition: all var(--transition);
  margin-left: 8px;
}

.nav .btn-theme:hover {
  background: var(--accent);
  color: var(--primary);
  border-color: var(--accent);
}

body.dark .nav .btn-theme {
  border-color: #555;
  color: #e0e0e0;
}

body.dark .nav .btn-theme:hover {
  background: var(--accent);
  color: #1a1a2e;
}

/* Hero Section */
.hero {
  background: linear-gradient(135deg, var(--hero-start) 0%, var(--hero-end) 100%);
  color: #fff;
  padding: 100px 24px;
  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% 50%, rgba(255, 215, 0, 0.08) 0%, transparent 50%),
              radial-gradient(circle at 70% 50%, rgba(255, 255, 255, 0.05) 0%, transparent 50%);
  animation: heroGlow 15s ease-in-out infinite alternate;
}

@keyframes heroGlow {
  0% { transform: translate(0, 0) rotate(0deg); }
  100% { transform: translate(20px, -20px) rotate(5deg); }
}

.hero h1 {
  font-size: 2.6rem;
  margin-bottom: 20px;
  position: relative;
  z-index: 1;
  text-shadow: 0 2px 20px rgba(0, 0, 0, 0.3);
  animation: fadeInUp 0.8s ease;
}

.hero p {
  font-size: 1.15rem;
  max-width: 700px;
  margin: 0 auto 28px;
  opacity: 0.9;
  position: relative;
  z-index: 1;
  animation: fadeInUp 0.8s ease 0.2s both;
}

.hero .btn {
  background: var(--accent);
  color: var(--primary);
  padding: 14px 36px;
  border-radius: 30px;
  font-weight: 700;
  display: inline-block;
  margin: 6px;
  font-size: 1rem;
  position: relative;
  z-index: 1;
  transition: transform var(--transition), box-shadow var(--transition);
  box-shadow: 0 4px 15px rgba(255, 215, 0, 0.3);
}

.hero .btn:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 25px rgba(255, 215, 0, 0.4);
  text-decoration: none;
}

.hero .btn:last-child {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border: 1px solid rgba(255, 255, 255, 0.3);
  color: #fff;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.hero .btn:last-child:hover {
  background: rgba(255, 255, 255, 0.25);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.3);
}

/* Sections */
.section {
  padding: 70px 24px;
  max-width: 1200px;
  margin: 0 auto;
  animation: fadeIn 0.6s ease;
}

.section h2 {
  font-size: 2rem;
  margin-bottom: 28px;
  border-left: 5px solid var(--accent);
  padding-left: 20px;
  color: var(--text);
  transition: color var(--transition);
  position: relative;
}

.section h2::after {
  content: '';
  position: absolute;
  bottom: -8px;
  left: 20px;
  width: 60px;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), transparent);
  border-radius: 2px;
}

.section p {
  color: var(--text-secondary);
  transition: color var(--transition);
  margin-bottom: 16px;
}

/* Grid */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
}

/* Cards */
.card {
  background: var(--bg-card);
  border-radius: 16px;
  padding: 28px;
  box-shadow: 0 2px 12px var(--shadow);
  transition: transform 0.4s ease, box-shadow 0.4s ease, background var(--transition);
  border: 1px solid transparent;
  position: relative;
  overflow: hidden;
}

.card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: linear-gradient(90deg, var(--accent), #ff8c00, var(--accent));
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.5s ease;
}

.card:hover::before {
  transform: scaleX(1);
}

.card:hover {
  transform: translateY(-6px);
  box-shadow: 0 12px 30px var(--shadow-hover);
  border-color: rgba(255, 215, 0, 0.2);
}

.card h3 {
  margin-bottom: 14px;
  font-size: 1.25rem;
  color: var(--text);
  transition: color var(--transition);
}

.card p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  transition: color var(--transition);
  margin-bottom: 0;
}

body.dark .card {
  background: var(--bg-card);
  box-shadow: 0 2px 12px var(--shadow);
}

body.dark .card:hover {
  box-shadow: 0 12px 30px var(--shadow-hover);
}

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

.faq-item {
  border-bottom: 1px solid var(--border);
  padding: 18px 0;
  cursor: pointer;
  transition: border-color var(--transition);
  background: var(--bg-card);
  border-radius: 12px;
  margin-bottom: 8px;
  padding: 18px 24px;
  box-shadow: 0 1px 4px var(--shadow);
}

.faq-question {
  font-weight: 600;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 1.05rem;
  color: var(--text);
  transition: color var(--transition);
}

.faq-question span {
  font-size: 1.4rem;
  color: var(--accent);
  transition: transform 0.3s ease;
}

.faq-item.active .faq-question span {
  transform: rotate(180deg);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.5s ease, opacity 0.4s ease, padding 0.4s ease;
  color: var(--text-secondary);
  margin-top: 0;
  opacity: 0;
  padding-top: 0;
}

.faq-item.active .faq-answer {
  max-height: 300px;
  opacity: 1;
  margin-top: 12px;
  padding-top: 12px;
  border-top: 1px solid var(--border);
}

/* HowTo Steps */
.howto-step {
  background: var(--bg-card);
  border-radius: 14px;
  padding: 20px 24px;
  margin-bottom: 14px;
  box-shadow: 0 2px 8px var(--shadow);
  transition: transform var(--transition), box-shadow var(--transition);
  display: flex;
  align-items: center;
  gap: 16px;
}

.howto-step:hover {
  transform: translateX(6px);
  box-shadow: 0 6px 20px var(--shadow-hover);
}

.howto-step .step-num {
  background: var(--accent);
  color: var(--primary);
  width: 38px;
  height: 38px;
  border-radius: 50%;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.1rem;
  flex-shrink: 0;
  box-shadow: 0 2px 8px rgba(255, 215, 0, 0.3);
}

.howto-step strong {
  color: var(--text);
  transition: color var(--transition);
}

/* Footer */
.footer {
  background: var(--footer-bg);
  color: #ccc;
  padding: 50px 24px 40px;
  text-align: center;
  font-size: 0.9rem;
  transition: background var(--transition);
  position: relative;
}

.footer::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 4px;
  background: linear-gradient(90deg, var(--accent), #ff8c00, var(--accent));
}

.footer a {
  color: var(--accent);
  transition: opacity var(--transition);
}

.footer a:hover {
  opacity: 0.8;
  text-decoration: none;
}

.footer .legal-links {
  margin: 20px 0;
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 20px;
}

.footer p {
  color: #aaa;
}

/* Back to Top */
.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  background: var(--primary);
  color: var(--accent);
  width: 48px;
  height: 48px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.4s ease, transform 0.3s ease, background var(--transition);
  z-index: 99;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
  border: none;
}

.back-to-top:hover {
  transform: translateY(-4px) scale(1.05);
  background: var(--accent);
  color: var(--primary);
}

.back-to-top.show {
  opacity: 1;
}

body.dark .back-to-top {
  background: #333;
  color: var(--accent);
}

body.dark .back-to-top:hover {
  background: var(--accent);
  color: #1a1a2e;
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(40px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Scroll-triggered animation (via IntersectionObserver in JS) */
.section {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.7s ease, transform 0.7s ease;
}

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

.card, .faq-item, .howto-step {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.5s ease, transform 0.5s ease, box-shadow 0.4s ease, border-color 0.4s ease;
}

.card.visible, .faq-item.visible, .howto-step.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Glass effect for certain elements */
.glass {
  background: var(--glass-bg);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--glass-border);
  box-shadow: var(--glass-shadow);
  border-radius: 16px;
}

/* Responsive */
@media (max-width: 1024px) {
  .hero h1 { font-size: 2.2rem; }
  .section { padding: 50px 20px; }
  .grid { gap: 20px; }
}

@media (max-width: 768px) {
  .hero { padding: 70px 20px; }
  .hero h1 { font-size: 1.8rem; }
  .hero p { font-size: 1rem; }
  .hero .btn { padding: 12px 28px; font-size: 0.95rem; }
  
  .nav { flex-direction: column; gap: 10px; padding: 10px 16px; }
  .nav .links { display: flex; flex-wrap: wrap; justify-content: center; gap: 4px; }
  .nav a { font-size: 0.85rem; margin: 0 4px; padding: 4px 10px; }
  .nav .btn-theme { margin-left: 4px; padding: 4px 12px; }
  .nav .logo { font-size: 1.3rem; }
  
  .section { padding: 40px 16px; }
  .section h2 { font-size: 1.6rem; padding-left: 14px; }
  .section h2::after { left: 14px; width: 40px; }
  
  .grid { grid-template-columns: 1fr; gap: 16px; }
  .card { padding: 20px; }
  .card h3 { font-size: 1.1rem; }
  
  .faq-item { padding: 14px 16px; }
  .faq-question { font-size: 0.95rem; }
  
  .howto-step { padding: 16px; gap: 12px; }
  .howto-step .step-num { width: 32px; height: 32px; font-size: 0.95rem; }
  
  .footer { padding: 30px 16px; }
  .footer .legal-links { gap: 12px; }
  
  .back-to-top { bottom: 20px; right: 20px; width: 42px; height: 42px; font-size: 1.1rem; }
}

@media (max-width: 480px) {
  .hero h1 { font-size: 1.5rem; }
  .hero p { font-size: 0.9rem; }
  .hero .btn { padding: 10px 20px; font-size: 0.85rem; margin: 4px; display: block; width: 80%; margin: 6px auto; }
  
  .section { padding: 30px 12px; }
  .section h2 { font-size: 1.3rem; }
  
  .nav { padding: 8px 12px; }
  .nav a { font-size: 0.75rem; padding: 3px 8px; }
  .nav .logo { font-size: 1.1rem; }
  
  .card { padding: 16px; }
  .card h3 { font-size: 1rem; }
  .card p { font-size: 0.85rem; }
}