/* ============================================================
   USDT(欧易)官网 - 主样式表
   数字资产/金融科技风格
   配色：深色背景 #0a1628 | USDT绿 #26a17b | 金色 #f0b90b | 白色
   ============================================================ */

/* === CSS Variables === */
:root {
  --bg-primary: #0a1628;
  --bg-secondary: #0d1f3c;
  --bg-card: #112240;
  --bg-input: #0d1f3c;
  --border-color: #1a3460;
  --text-primary: #ffffff;
  --text-secondary: #a8b2d1;
  --text-muted: #6c7a9c;
  --usdt-green: #26a17b;
  --usdt-green-hover: #1e8465;
  --usdt-green-light: rgba(38, 161, 123, 0.15);
  --gold: #f0b90b;
  --gold-hover: #d4a30a;
  --gold-light: rgba(240, 185, 11, 0.15);
  --gradient-hero: linear-gradient(135deg, #0a1628 0%, #0d1f3c 50%, #112240 100%);
  --gradient-green: linear-gradient(135deg, #26a17b 0%, #1e8465 100%);
  --gradient-gold: linear-gradient(135deg, #f0b90b 0%, #d4a30a 100%);
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 20px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 40px rgba(0, 0, 0, 0.5);
  --shadow-green: 0 4px 20px rgba(38, 161, 123, 0.3);
  --shadow-gold: 0 4px 20px rgba(240, 185, 11, 0.3);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-xl: 28px;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --max-width: 1200px;
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", "Helvetica Neue", sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
}

a {
  color: var(--usdt-green);
  text-decoration: none;
  transition: color var(--transition);
}
a:hover {
  color: var(--usdt-green-hover);
}

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

ul, ol {
  list-style: none;
}

.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 20px;
}

/* === Typography === */
h1, h2, h3, h4, h5, h6 {
  line-height: 1.3;
  font-weight: 700;
}

h1 {
  font-size: clamp(2rem, 5vw, 3.2rem);
}

h2 {
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  text-align: center;
  margin-bottom: 1rem;
}

h3 {
  font-size: clamp(1.1rem, 2vw, 1.4rem);
}

.section-subtitle {
  text-align: center;
  color: var(--text-secondary);
  font-size: 1.05rem;
  margin-bottom: 3rem;
}

/* === Header & Navigation === */
header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: rgba(10, 22, 40, 0.95);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-color);
  transition: background var(--transition);
}

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: 800;
  color: var(--text-primary);
  letter-spacing: 1px;
}
.logo span {
  color: var(--usdt-green);
}

nav ul {
  display: flex;
  align-items: center;
  gap: 8px;
}

nav a {
  display: block;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 500;
  transition: all var(--transition);
}
nav a:hover,
nav a.active {
  color: var(--usdt-green);
  background: var(--usdt-green-light);
}

.nav-download {
  background: var(--gradient-green) !important;
  color: #fff !important;
  font-weight: 700 !important;
  border-radius: var(--radius-xl) !important;
  padding: 10px 22px !important;
}
.nav-download:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-green);
  color: #fff !important;
}

/* Mobile menu toggle */
.menu-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 10px;
  background: none;
  border: none;
}
.menu-toggle span {
  display: block;
  width: 25px;
  height: 2px;
  background: var(--text-primary);
  transition: var(--transition);
}

/* === Hero Section === */
#hero {
  position: relative;
  min-height: 85vh;
  display: flex;
  align-items: center;
  background: var(--gradient-hero);
  overflow: hidden;
  padding: 60px 0;
}

#hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(38, 161, 123, 0.12) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

#hero::after {
  content: '';
  position: absolute;
  bottom: -30%;
  left: -10%;
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, rgba(240, 185, 11, 0.1) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

#hero .container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
  align-items: center;
  position: relative;
  z-index: 1;
}

.hero-content h1 {
  margin-bottom: 1.2rem;
  background: linear-gradient(135deg, var(--text-primary) 0%, var(--usdt-green) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-content .hero-desc {
  font-size: 1.1rem;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  max-width: 480px;
}

.hero-badges {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 2.5rem;
}

.hero-badges .badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-xl);
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.hero-badges .badge .dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--usdt-green);
  animation: pulse-dot 2s infinite;
}

.hero-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
}

.hero-image {
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero-image img {
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  max-width: 420px;
  animation: float 6s ease-in-out infinite;
}

/* === Buttons === */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 14px 32px;
  border: none;
  border-radius: var(--radius-xl);
  font-size: 1rem;
  font-weight: 700;
  cursor: pointer;
  transition: all var(--transition);
  text-decoration: none;
}

.btn-primary {
  background: var(--gradient-green);
  color: #fff;
  box-shadow: var(--shadow-green);
}
.btn-primary:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 30px rgba(38, 161, 123, 0.45);
  color: #fff;
}

.btn-gold {
  background: var(--gradient-gold);
  color: #1a1a2e;
  box-shadow: var(--shadow-gold);
}
.btn-gold:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 30px rgba(240, 185, 11, 0.45);
  color: #1a1a2e;
}

.btn-outline {
  background: transparent;
  color: var(--text-primary);
  border: 2px solid var(--border-color);
}
.btn-outline:hover {
  border-color: var(--usdt-green);
  color: var(--usdt-green);
  transform: translateY(-2px);
}

.btn-sm {
  padding: 10px 22px;
  font-size: 0.9rem;
}

.btn-lg {
  padding: 18px 40px;
  font-size: 1.1rem;
}

/* === Sections === */
section {
  padding: 80px 0;
}

section:nth-child(even) {
  background: var(--bg-secondary);
}

/* === Features Section === */
#features .features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 24px;
}

.feature-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 32px 28px;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.feature-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--gradient-green);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--transition);
}

.feature-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-md);
  border-color: var(--usdt-green);
}

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

.feature-icon {
  width: 56px;
  height: 56px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.6rem;
  margin-bottom: 1.2rem;
}

.feature-icon.green {
  background: var(--usdt-green-light);
  color: var(--usdt-green);
}

.feature-icon.gold {
  background: var(--gold-light);
  color: var(--gold);
}

.feature-card h3 {
  margin-bottom: 0.6rem;
}

.feature-card p {
  color: var(--text-secondary);
  font-size: 0.95rem;
}

/* === Services Section === */
#services .services-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 24px;
}

.service-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 36px 28px;
  transition: all var(--transition);
}

.service-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--gold);
}

.service-card h3 {
  color: var(--gold);
  margin-bottom: 1rem;
}

.service-card p {
  color: var(--text-secondary);
  font-size: 0.95rem;
}

/* === CTA Section === */
#cta {
  background: var(--gradient-hero);
  text-align: center;
  position: relative;
  overflow: hidden;
}

#cta::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(38, 161, 123, 0.15) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

#cta .container {
  position: relative;
  z-index: 1;
}

#cta h2 {
  margin-bottom: 1rem;
}

#cta .cta-desc {
  font-size: 1.1rem;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}

.cta-buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 16px;
}

/* === Price Ticker === */
.price-section {
  padding: 40px 0;
}

.price-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 20px;
}

.price-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 24px;
  display: flex;
  align-items: center;
  gap: 16px;
  transition: all var(--transition);
}

.price-card:hover {
  border-color: var(--gold);
  box-shadow: var(--shadow-sm);
}

.price-icon {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  font-weight: 700;
  flex-shrink: 0;
}

.price-icon.btc {
  background: rgba(240, 185, 11, 0.2);
  color: var(--gold);
}

.price-icon.eth {
  background: rgba(98, 126, 234, 0.2);
  color: #627eea;
}

.price-info .price-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.price-info .price-value {
  font-size: 1.4rem;
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.price-info .price-change {
  font-size: 0.85rem;
  font-weight: 600;
}

.price-change.up {
  color: var(--usdt-green);
}

.price-change.down {
  color: #e15241;
}

/* === News Section === */
.news-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 20px;
}

.news-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: all var(--transition);
}

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

.news-card img {
  width: 100%;
  height: 180px;
  object-fit: cover;
}

.news-card-body {
  padding: 20px;
}

.news-card-body .news-date {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.news-card-body h3 {
  font-size: 1.05rem;
  margin-bottom: 8px;
}

.news-card-body p {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* === About Page === */
.timeline {
  position: relative;
  padding-left: 30px;
  margin: 40px 0;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--border-color);
}

.timeline-item {
  position: relative;
  margin-bottom: 32px;
  padding-left: 24px;
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: -34px;
  top: 4px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--usdt-green);
  border: 3px solid var(--bg-secondary);
}

.timeline-year {
  font-size: 0.85rem;
  color: var(--usdt-green);
  font-weight: 700;
  margin-bottom: 4px;
}

.timeline-item h3 {
  margin-bottom: 6px;
}

.timeline-item p {
  color: var(--text-secondary);
  font-size: 0.95rem;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 20px;
  margin: 40px 0;
}

.stat-item {
  text-align: center;
  padding: 28px 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
}

.stat-number {
  font-size: 2.4rem;
  font-weight: 800;
  color: var(--usdt-green);
  line-height: 1;
  margin-bottom: 8px;
}

.stat-label {
  font-size: 0.9rem;
  color: var(--text-secondary);
}

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

details.faq-item {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  margin-bottom: 12px;
  transition: all var(--transition);
}

details.faq-item:hover {
  border-color: var(--usdt-green);
}

details.faq-item summary {
  padding: 18px 24px;
  cursor: pointer;
  font-weight: 600;
  font-size: 1.02rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
  list-style: none;
}

details.faq-item summary::-webkit-details-marker {
  display: none;
}

details.faq-item summary .faq-arrow {
  transition: transform var(--transition);
  font-size: 0.7rem;
  color: var(--text-muted);
}

details.faq-item[open] summary .faq-arrow {
  transform: rotate(180deg);
  color: var(--usdt-green);
}

details.faq-item .faq-answer {
  padding: 0 24px 20px 24px;
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.8;
}

/* === Contact Page === */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 40px;
}

.contact-form {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 32px;
}

.form-group {
  margin-bottom: 20px;
}

.form-group label {
  display: block;
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 6px;
  color: var(--text-secondary);
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 12px 16px;
  background: var(--bg-input);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-size: 0.95rem;
  font-family: inherit;
  transition: border-color var(--transition);
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--usdt-green);
  box-shadow: 0 0 0 3px var(--usdt-green-light);
}

.contact-info {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.contact-info-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 24px;
  display: flex;
  align-items: flex-start;
  gap: 16px;
}

.contact-info-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  flex-shrink: 0;
  background: var(--usdt-green-light);
  color: var(--usdt-green);
}

.contact-info-card h4 {
  margin-bottom: 4px;
  font-size: 0.95rem;
}

.contact-info-card p {
  color: var(--text-secondary);
  font-size: 0.9rem;
}

/* === Footer === */
footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: 50px 0 30px;
}

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

.footer-col h4 {
  font-size: 1rem;
  margin-bottom: 16px;
  color: var(--text-primary);
}

.footer-col p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.7;
}

.footer-col ul li {
  margin-bottom: 8px;
}

.footer-col ul li a {
  color: var(--text-secondary);
  font-size: 0.9rem;
  transition: color var(--transition);
}

.footer-col ul li a:hover {
  color: var(--usdt-green);
}

.footer-bottom {
  border-top: 1px solid var(--border-color);
  padding-top: 24px;
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* === Animations === */
@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-20px); }
}

@keyframes pulse-dot {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.4; }
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(30px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeInLeft {
  from {
    opacity: 0;
    transform: translateX(-30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes fadeInRight {
  from {
    opacity: 0;
    transform: translateX(30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes scaleIn {
  from {
    opacity: 0;
    transform: scale(0.9);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: all 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

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

.reveal-left {
  opacity: 0;
  transform: translateX(-30px);
  transition: all 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

.reveal-left.visible {
  opacity: 1;
  transform: translateX(0);
}

.reveal-right {
  opacity: 0;
  transform: translateX(30px);
  transition: all 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

.reveal-right.visible {
  opacity: 1;
  transform: translateX(0);
}

/* ============================================================
   Responsive Design
   ============================================================ */
@media (max-width: 1024px) {
  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }

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

  #hero .container {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-content .hero-desc {
    max-width: 100%;
  }

  .hero-badges,
  .hero-buttons {
    justify-content: center;
  }

  .hero-image {
    order: -1;
  }

  .hero-image img {
    max-width: 280px;
  }
}

@media (max-width: 768px) {
  header .container {
    height: 60px;
  }

  .menu-toggle {
    display: flex;
  }

  nav {
    position: fixed;
    top: 60px;
    left: 0;
    right: 0;
    background: rgba(10, 22, 40, 0.98);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border-color);
    padding: 16px 0;
    transform: translateY(-120%);
    transition: transform var(--transition);
    z-index: 999;
  }

  nav.open {
    transform: translateY(0);
  }

  nav ul {
    flex-direction: column;
    gap: 4px;
  }

  nav a {
    padding: 12px 24px;
    font-size: 1rem;
  }

  section {
    padding: 50px 0;
  }

  #hero {
    min-height: auto;
    padding: 40px 0 60px;
  }

  .hero-content h1 {
    font-size: 1.8rem;
  }

  .features-grid,
  .services-grid {
    grid-template-columns: 1fr;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 24px;
  }

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

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

  .btn {
    padding: 12px 24px;
    font-size: 0.95rem;
  }
}

@media (max-width: 480px) {
  .container {
    padding: 0 16px;
  }

  h2 {
    font-size: 1.4rem;
  }

  .hero-image img {
    max-width: 220px;
  }

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

  .cta-buttons {
    flex-direction: column;
    align-items: center;
  }

  .hero-buttons {
    flex-direction: column;
    align-items: center;
  }
}