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

:root {
  --navy: #0f1923;
  --navy-light: #1a2636;
  --blue: #3d6b8e;
  --blue-light: #4d7fa6;
  --accent: #c85a3a;
  --accent-light: #e8a08c;
  --white: #faf9f5;
  --gray-50: #f4f3ef;
  --gray-100: #eae9e4;
  --gray-200: #e0ded6;
  --gray-400: #8a8880;
  --gray-600: #5a5850;
  --gray-800: #2a2925;
  --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-zh: 'PingFang SC', 'Microsoft YaHei', 'Noto Sans SC', sans-serif;
  --radius: 12px;
  --shadow: 0 4px 24px rgba(0,0,0,0.06);
  --shadow-hover: 0 12px 40px rgba(0,0,0,0.1);
}

html { scroll-behavior: smooth; }
body { font-family: var(--font); color: var(--gray-800); line-height: 1.6; background: var(--white); -webkit-font-smoothing: antialiased; }
body.zh { font-family: var(--font-zh); }
a { color: var(--blue); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--blue-light); }
img { max-width: 100%; height: auto; display: block; }
.container { max-width: 1160px; margin: 0 auto; padding: 0 24px; }

/* ===== Reveal Animation ===== */
.reveal { opacity: 0; transform: translateY(24px); transition: opacity 0.6s ease, transform 0.6s ease; }
.reveal.visible { opacity: 1; transform: translateY(0); }
.reveal:nth-child(2) { transition-delay: 0.1s; }
.reveal:nth-child(3) { transition-delay: 0.2s; }
.reveal:nth-child(4) { transition-delay: 0.3s; }
.reveal:nth-child(5) { transition-delay: 0.4s; }

/* ===== Navigation ===== */
.nav { position: fixed; top: 0; left: 0; right: 0; z-index: 1000; background: transparent; transition: background 0.3s, box-shadow 0.3s; }
.nav.scrolled { background: var(--navy); box-shadow: 0 2px 20px rgba(0,0,0,0.3); }
.nav-inner { max-width: 1160px; margin: 0 auto; padding: 0 24px; display: flex; align-items: center; justify-content: space-between; height: 72px; }
.nav-logo-img { height: 44px; width: auto; }
.nav-links { display: flex; list-style: none; gap: 32px; align-items: center; }
.nav-links a { color: var(--white); font-size: 15px; font-weight: 500; letter-spacing: 0.3px; opacity: 0.85; transition: opacity 0.2s, color 0.2s; }
.nav-links a:hover { opacity: 1; color: var(--white); }
/* Active section — peach/accent-light; mirrors DRIVEResearch data platform
   top-nav active style. JS scrollspy in scripts.js toggles .active. */
.nav-links > li > a.active { opacity: 1; color: var(--accent-light); }

.lang-switch { display: inline-flex; border: 1px solid rgba(255,255,255,0.3); border-radius: 20px; overflow: hidden; margin-left: 8px; }
.lang-switch a { padding: 4px 12px; font-size: 12px; font-weight: 600; text-transform: none; letter-spacing: 0; opacity: 1; }
.lang-switch a.active { background: rgba(255,255,255,0.2); }

.nav-toggle { display: none; flex-direction: column; gap: 5px; background: none; border: none; cursor: pointer; padding: 4px; }
.nav-toggle span { display: block; width: 22px; height: 2px; background: var(--white); }

/* ===== Buttons ===== */
.btn { display: inline-block; padding: 12px 28px; font-size: 15px; font-weight: 600; border-radius: 6px; transition: all 0.2s; cursor: pointer; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: #b04e30; color: #fff; transform: translateY(-1px); }
.btn-outline { border: 1.5px solid rgba(255,255,255,0.3); color: var(--white); }
.btn-outline:hover { border-color: var(--white); color: var(--white); }
.btn-outline-dark { border: 1.5px solid var(--gray-200); color: var(--gray-800); }
.btn-outline-dark:hover { border-color: var(--blue); color: var(--blue); }

/* ===== Section Titles ===== */
.section-title { font-size: clamp(28px, 4vw, 40px); font-weight: 700; text-align: center; margin-bottom: 12px; letter-spacing: -0.3px; }
.section-subtitle { text-align: center; color: var(--gray-600); font-size: 16px; max-width: 640px; margin: 0 auto 56px; line-height: 1.7; }

/* ===== Hero ===== */
.hero { position: relative; min-height: 100vh; display: flex; align-items: center; justify-content: center; background: var(--navy); overflow: hidden; }
.hero-bg { position: absolute; inset: 0; width: 100%; height: 100%; object-fit: cover; object-position: center; }
.hero-overlay { position: absolute; inset: 0; background: linear-gradient(135deg, rgba(10,22,40,0.78) 0%, rgba(19,32,57,0.65) 50%, rgba(10,22,40,0.72) 100%); }
.hero-content { position: relative; z-index: 1; text-align: center; max-width: 760px; padding: 0 24px; }
.hero h1 { font-size: clamp(30px, 5vw, 52px); font-weight: 700; color: var(--white); line-height: 1.2; margin-bottom: 20px; }
.hero-desc { font-size: 17px; color: var(--gray-400); line-height: 1.7; margin-bottom: 36px; max-width: 580px; margin-left: auto; margin-right: auto; }
.hero-actions { display: flex; gap: 16px; justify-content: center; flex-wrap: wrap; }

/* ===== Overview Stats ===== */
.overview { padding: 100px 0; background: var(--white); }
.stats-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
.stat-card { text-align: center; padding: 40px 16px; border-radius: var(--radius); border: 1px solid var(--gray-200); background: var(--white); transition: transform 0.3s, box-shadow 0.3s; }
.stat-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-hover); }
.stat-number { font-size: 40px; font-weight: 700; color: var(--navy); margin-bottom: 4px; }
.stat-label { font-size: 14px; font-weight: 600; color: var(--blue); text-transform: uppercase; letter-spacing: 0.5px; margin-bottom: 8px; }
.stat-desc { font-size: 13px; color: var(--gray-600); line-height: 1.5; }

/* ===== Framework ===== */
.framework { padding: 100px 0; background: var(--gray-50); }
.framework-img { max-width: 800px; margin: 0 auto 48px; border-radius: var(--radius); }
.framework-cols { display: grid; grid-template-columns: 1fr 1fr; gap: 28px; margin-bottom: 40px; }
.framework-card { padding: 32px; border-radius: var(--radius); border: 1px solid var(--gray-200); background: var(--white); }
.framework-card.highlight { border-left: 4px solid var(--accent); }
.framework-card h3 { font-size: 20px; font-weight: 700; margin-bottom: 12px; color: var(--navy); }
.framework-card p { font-size: 14px; color: var(--gray-600); line-height: 1.7; }
.framework-callout { text-align: center; padding: 28px; background: var(--navy); color: var(--white); border-radius: var(--radius); font-size: 17px; font-weight: 500; line-height: 1.6; }
.eval-dims { display: flex; gap: 16px; justify-content: center; margin-top: 32px; flex-wrap: wrap; }
.eval-dim { padding: 10px 24px; border-radius: 24px; background: var(--white); border: 1px solid var(--gray-200); font-size: 14px; font-weight: 600; color: var(--blue); }

/* ===== Data Section ===== */
.data-section { padding: 100px 0; background: var(--navy); color: var(--white); }
.data-section .section-title { color: var(--white); }
.data-section .section-subtitle { color: var(--gray-400); }
.data-gallery { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; margin-bottom: 48px; }
.data-img { width: 100%; height: 260px; object-fit: cover; border-radius: var(--radius); border: 1px solid rgba(255,255,255,0.1); }
.data-banner { width: 100%; border-radius: var(--radius); margin-bottom: 20px; border: 1px solid rgba(255,255,255,0.1); }
.scene-labels { display: flex; flex-wrap: wrap; gap: 8px; justify-content: center; margin-bottom: 12px; }
.scene-tag { padding: 5px 14px; font-size: 12px; font-weight: 500; color: var(--gray-400); background: rgba(255,255,255,0.06); border: 1px solid rgba(255,255,255,0.1); border-radius: 20px; }
.scene-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 16px; margin-bottom: 20px; }
.scene-item { text-align: center; }
.scene-item img { width: 100%; border-radius: var(--radius); border: 1px solid rgba(255,255,255,0.1); aspect-ratio: 2/1; object-fit: cover; }
.scene-item-label { margin-top: 8px; font-size: 12px; font-weight: 500; color: var(--gray-400); }
@media (max-width: 900px) { .scene-grid { grid-template-columns: repeat(3, 1fr); } }
@media (max-width: 480px) { .scene-grid { grid-template-columns: repeat(2, 1fr); } }
.data-caption { text-align: center; font-size: 14px; color: var(--gray-400); margin-bottom: 48px; font-style: italic; }

.data-features { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.data-feature { background: rgba(255,255,255,0.04); border: 1px solid rgba(255,255,255,0.08); padding: 28px; border-radius: var(--radius); }
.data-feature h3 { font-size: 17px; font-weight: 700; color: var(--white); margin-bottom: 16px; padding-bottom: 12px; border-bottom: 2px solid var(--accent); }
.param-list { list-style: none; }
.param-list li { padding: 5px 0; font-size: 13px; color: var(--gray-400); line-height: 1.5; padding-left: 14px; position: relative; }
.param-list li::before { content: ''; position: absolute; left: 0; top: 12px; width: 5px; height: 5px; border-radius: 50%; background: var(--accent); opacity: 0.5; }

/* ===== Open Datasets ===== */
.datasets { padding: 100px 0; background: var(--white); }
.datasets-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
.dataset-card { border-radius: var(--radius); border: 1px solid var(--gray-200); overflow: hidden; transition: transform 0.3s, box-shadow 0.3s; }
.dataset-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-hover); }
.dataset-card img { width: 100%; height: auto; }
.dataset-card-body { padding: 24px; }
.dataset-card h3 { font-size: 20px; font-weight: 700; color: var(--navy); margin-bottom: 4px; }
.dataset-badge { display: inline-block; font-size: 11px; font-weight: 600; color: var(--accent); background: rgba(200,90,58,0.08); padding: 3px 10px; border-radius: 12px; margin-bottom: 12px; }
.dataset-card p { font-size: 14px; color: var(--gray-600); line-height: 1.6; margin-bottom: 16px; }
.dataset-link { font-size: 14px; font-weight: 600; color: var(--blue); }

/* ===== Applications ===== */
.applications { padding: 100px 0; background: var(--gray-50); }
.app-visual { max-width: 800px; margin: 0 auto 48px; border-radius: var(--radius); }
.app-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.app-card { padding: 28px; border-radius: var(--radius); border: 1px solid var(--gray-200); background: var(--white); transition: transform 0.3s, box-shadow 0.3s; }
.app-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-hover); }
.app-number { font-size: 36px; font-weight: 700; color: var(--accent); opacity: 0.25; line-height: 1; margin-bottom: 8px; }
.app-card h3 { font-size: 17px; font-weight: 700; color: var(--navy); margin-bottom: 4px; }
.app-zh { font-size: 13px; color: var(--blue); margin-bottom: 12px; }
.app-card p:last-child { font-size: 13px; color: var(--gray-600); line-height: 1.6; }

/* ===== About ===== */
.about { padding: 100px 0; background: var(--white); }
.about-banner { width: 100%; border-radius: var(--radius); margin-bottom: 40px; }
.about-content { display: grid; grid-template-columns: 2fr 1fr; gap: 40px; align-items: start; }
.about-text p { font-size: 15px; color: var(--gray-600); line-height: 1.8; margin-bottom: 16px; }
.about-text strong { color: var(--gray-800); }
.affiliations { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; margin-top: 28px; }
.affiliation { padding: 20px; background: var(--gray-50); border-radius: 8px; }
.affiliation h4 { font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.5px; color: var(--blue); margin-bottom: 8px; }
.affiliation p { font-size: 13px; color: var(--gray-600); line-height: 1.5; margin-bottom: 0; }
.standards-box { background: var(--navy); color: var(--white); padding: 28px; border-radius: var(--radius); }
.standards-box h3 { font-size: 17px; font-weight: 600; margin-bottom: 16px; }
.standards-box ul { list-style: none; }
.standards-box li { padding: 9px 0; font-size: 14px; color: var(--gray-400); border-bottom: 1px solid rgba(255,255,255,0.06); }
.standards-box li:last-child { border-bottom: none; }

/* ===== Contact ===== */
.contact { padding: 100px 0; background: var(--gray-50); }
.contact-layout { display: flex; gap: 48px; align-items: center; justify-content: center; max-width: 800px; margin: 0 auto; }
.contact-info { flex: 1; }
.contact-item { padding: 20px 0; border-bottom: 1px solid var(--gray-200); }
.contact-item:last-child { border-bottom: none; }
.contact-item h3 { font-size: 13px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.5px; color: var(--blue); margin-bottom: 8px; }
.contact-item p { font-size: 15px; color: var(--gray-600); line-height: 1.7; }
.contact-qr-group { display: flex; gap: 24px; flex-shrink: 0; }
.contact-qr { text-align: center; }
.contact-qr img { width: 160px; height: 160px; border-radius: var(--radius); border: 1px solid var(--gray-200); margin-bottom: 8px; }
.contact-qr p { font-size: 13px; color: var(--gray-400); font-weight: 500; }

/* ===== Footer ===== */
.footer { background: var(--navy); padding: 24px 0; }
.footer-inner { display: flex; justify-content: space-between; align-items: center; }
.footer p { font-size: 13px; color: var(--gray-400); }

/* ===== Responsive ===== */
@media (max-width: 900px) {
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .framework-cols, .data-features, .app-grid { grid-template-columns: 1fr; }
  .datasets-grid { grid-template-columns: 1fr 1fr; }
  .about-content { grid-template-columns: 1fr; }
  .affiliations { grid-template-columns: 1fr; }
  .contact-layout { flex-direction: column; text-align: center; }
  .app-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 640px) {
  .nav-links { display: none; position: absolute; top: 64px; left: 0; right: 0; background: var(--navy); flex-direction: column; padding: 16px 24px; gap: 16px; }
  .nav-links.open { display: flex; }
  .nav-toggle { display: flex; }
  .stats-grid { grid-template-columns: 1fr 1fr; gap: 12px; }
  .stat-card { padding: 24px 12px; }
  .stat-number { font-size: 28px; }
  .app-grid { grid-template-columns: 1fr; }
  .footer-inner { flex-direction: column; gap: 8px; text-align: center; }
}