/* YanLan Turing — minimal monochrome, OpenAI-inspired */
:root {
  --bg: #ffffff;
  --bg-alt: #f7f7f8;
  --ink: #0d0d0d;
  --ink-soft: #565656;
  --line: #e6e6e6;
  --radius: 14px;
  --max: 1120px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue",
          "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", Arial, sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
a { color: inherit; text-decoration: none; }
.container { max-width: var(--max); margin: 0 auto; padding: 0 28px; }

/* ---------- Nav ---------- */
.nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: rgba(255,255,255,.82);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid transparent;
  transition: border-color .3s;
}
.nav.scrolled { border-bottom-color: var(--line); }
.nav-inner {
  max-width: var(--max); margin: 0 auto; padding: 0 28px;
  height: 64px; display: flex; align-items: center; gap: 40px;
}
.logo {
  display: flex; align-items: center; gap: 10px;
  font-weight: 700; font-size: 17px; letter-spacing: .01em;
}
.nav-links { display: flex; gap: 28px; font-size: 14.5px; color: var(--ink-soft); }
.nav-links a { transition: color .2s; }
.nav-links a:hover { color: var(--ink); }
.nav-actions { margin-left: auto; display: flex; align-items: center; gap: 14px; }
.lang-toggle {
  font: inherit; font-size: 13px; font-weight: 600;
  border: 1px solid var(--line); background: none; color: var(--ink-soft);
  border-radius: 99px; padding: 5px 12px; cursor: pointer;
  transition: all .2s;
}
.lang-toggle:hover { border-color: var(--ink); color: var(--ink); }

/* ---------- Buttons ---------- */
.btn {
  display: inline-block; border-radius: 99px; font-weight: 600;
  font-size: 15px; padding: 12px 26px; transition: all .2s; border: 1px solid transparent;
}
.btn-sm { padding: 8px 18px; font-size: 13.5px; }
.btn-dark { background: var(--ink); color: #fff; }
.btn-dark:hover { background: #333; }
.btn-ghost { border-color: var(--line); color: var(--ink); }
.btn-ghost:hover { border-color: var(--ink); }
.btn-light { background: #fff; color: var(--ink); }
.btn-light:hover { background: #e8e8e8; }

/* ---------- Hero ---------- */
.hero { padding: 200px 0 130px; }
.hero-title {
  font-size: clamp(44px, 7.2vw, 88px);
  line-height: 1.08; font-weight: 700; letter-spacing: -.03em;
  max-width: 900px;
}
.hero-sub {
  margin-top: 28px; font-size: clamp(17px, 2vw, 21px);
  color: var(--ink-soft); max-width: 560px;
}
.hero-actions { margin-top: 44px; display: flex; gap: 16px; flex-wrap: wrap; }

/* ---------- Statement ---------- */
.statement { padding: 110px 0; border-top: 1px solid var(--line); }
.statement p {
  font-size: clamp(24px, 3.4vw, 40px); font-weight: 600;
  line-height: 1.45; letter-spacing: -.015em; text-align: center;
}

/* ---------- Sections ---------- */
.section { padding: 110px 0; border-top: 1px solid var(--line); }
.section-alt { background: var(--bg-alt); }
.section-head { margin-bottom: 64px; max-width: 640px; }
.eyebrow {
  display: inline-block; font-size: 13px; font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: var(--ink-soft); margin-bottom: 16px;
}
.section h2 {
  font-size: clamp(30px, 4.2vw, 48px);
  font-weight: 700; letter-spacing: -.02em; line-height: 1.15;
}

/* ---------- Grids & Cards ---------- */
.grid { display: grid; gap: 24px; }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-2 { grid-template-columns: repeat(2, 1fr); }

.card {
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 36px 30px; transition: transform .25s, box-shadow .25s;
  background: var(--bg);
}
.card:hover { transform: translateY(-4px); box-shadow: 0 16px 40px rgba(0,0,0,.07); }
.card-num { font-size: 13px; color: var(--ink-soft); font-weight: 600; margin-bottom: 40px; }
.card h3 { font-size: 21px; font-weight: 700; margin-bottom: 12px; letter-spacing: -.01em; }
.card p { font-size: 15px; color: var(--ink-soft); }

.feature {
  background: var(--bg); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 40px 34px; display: flex; flex-direction: column; align-items: flex-start;
  transition: transform .25s, box-shadow .25s;
}
.feature:hover { transform: translateY(-4px); box-shadow: 0 16px 40px rgba(0,0,0,.07); }
.feature h3 { font-size: 22px; font-weight: 700; margin-bottom: 12px; letter-spacing: -.01em; }
.feature p { font-size: 15px; color: var(--ink-soft); flex: 1; }
.tag {
  margin-top: 24px; font-size: 12.5px; font-weight: 600;
  border: 1px solid var(--line); border-radius: 99px; padding: 4px 12px;
  color: var(--ink-soft);
}
.tag-link {
  color: var(--ink); text-decoration: none;
  transition: background .2s, color .2s, border-color .2s;
}
.tag-link:hover { background: var(--ink); color: var(--bg); border-color: var(--ink); }

/* ---------- About ---------- */
.about-grid {
  display: grid; grid-template-columns: 1fr 1.2fr; gap: 60px;
  align-items: start; margin-bottom: 80px;
}
.about-body p { color: var(--ink-soft); font-size: 16.5px; }
.about-body p + p { margin-top: 20px; }
.stats {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px;
  border-top: 1px solid var(--line); padding-top: 48px;
}
.stat-num { font-size: 40px; font-weight: 700; letter-spacing: -.02em; }
.stat-label { color: var(--ink-soft); font-size: 14.5px; margin-top: 6px; }

/* ---------- Contact ---------- */
.section-dark { background: var(--ink); color: #fff; }
.contact-inner { text-align: center; padding: 30px 28px; }
.contact-inner h2 { font-size: clamp(32px, 4.6vw, 54px); }
.contact-inner p { color: #b0b0b0; margin: 24px auto 40px; max-width: 480px; font-size: 17px; }

/* ---------- Footer ---------- */
.footer { padding: 64px 0 36px; border-top: 1px solid var(--line); }
.footer-grid {
  display: grid; grid-template-columns: 1.6fr 1fr 1fr 1fr;
  gap: 40px; margin-bottom: 56px;
}
.footer-brand { font-weight: 700; display: flex; align-items: baseline; gap: 10px; }
.footer-en { color: var(--ink-soft); font-weight: 500; font-size: 13.5px; }
.footer-tagline { color: var(--ink-soft); font-size: 14px; margin-top: 12px; }
.footer-col h4 {
  font-size: 13.5px; font-weight: 600; margin-bottom: 16px;
  letter-spacing: .02em;
}
.footer-col a {
  display: block; font-size: 13.5px; color: var(--ink-soft);
  padding: 5px 0; transition: color .2s;
}
.footer-col a:hover { color: var(--ink); }
.footer-bottom {
  border-top: 1px solid var(--line); padding-top: 24px;
  display: flex; justify-content: space-between; align-items: center;
  flex-wrap: wrap; gap: 10px;
  color: var(--ink-soft); font-size: 13px;
}
.footer-bottom a { color: var(--ink-soft); transition: color .2s; }
.footer-bottom a:hover { color: var(--ink); }

/* ---------- Reveal animation ---------- */
.reveal { opacity: 0; transform: translateY(24px); transition: opacity .7s ease, transform .7s ease; }
.reveal.visible { opacity: 1; transform: none; }

/* ---------- Responsive ---------- */
@media (max-width: 900px) {
  .grid-3 { grid-template-columns: 1fr; }
  .grid-2 { grid-template-columns: 1fr; }
  .about-grid { grid-template-columns: 1fr; gap: 28px; margin-bottom: 56px; }
  .nav-links { display: none; }
  .hero { padding: 150px 0 90px; }
  .section, .statement { padding: 80px 0; }
  .stats { grid-template-columns: 1fr; gap: 32px; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 32px; }
}

/* ---------- Mobile nav (hamburger) ---------- */
.nav-burger {
  display: none; flex-direction: column; justify-content: center; gap: 5px;
  width: 40px; height: 40px; padding: 9px 8px; margin-left: 4px;
  background: none; border: 1px solid var(--line); border-radius: 10px;
  cursor: pointer;
}
.nav-burger span {
  display: block; height: 2px; width: 100%; background: var(--ink);
  border-radius: 2px; transition: transform .25s, opacity .25s;
}
body.nav-open .nav-burger span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
body.nav-open .nav-burger span:nth-child(2) { opacity: 0; }
body.nav-open .nav-burger span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

@media (max-width: 900px) {
  .nav-burger { display: flex; }
  /* 手机端把导航链接做成下拉抽屉 */
  .nav-links {
    display: flex; flex-direction: column; gap: 0;
    position: fixed; top: 64px; left: 0; right: 0;
    background: rgba(255,255,255,.98);
    backdrop-filter: saturate(180%) blur(14px);
    -webkit-backdrop-filter: saturate(180%) blur(14px);
    border-bottom: 1px solid var(--line);
    padding: 8px 0; font-size: 16px;
    transform: translateY(-12px); opacity: 0; pointer-events: none;
    transition: transform .25s ease, opacity .25s ease;
  }
  body.nav-open .nav-links { transform: translateY(0); opacity: 1; pointer-events: auto; }
  .nav-links a {
    padding: 14px 28px; color: var(--ink);
    border-bottom: 1px solid var(--bg-alt);
  }
  .nav-links a:last-child { border-bottom: none; }
  /* 手机端隐藏"与我们合作"按钮上的多余间距压力，语言按钮保留 */
  .nav-actions .btn-dark.btn-sm { display: none; }
}

/* ---------- Small phones (≤480px) ---------- */
@media (max-width: 480px) {
  .container, .nav-inner { padding-left: 20px; padding-right: 20px; }
  .hero { padding: 120px 0 70px; }
  .hero-actions { gap: 12px; }
  .hero-actions .btn { width: 100%; text-align: center; }
  .section, .statement { padding: 60px 0; }
  .section-head { margin-bottom: 40px; }
  .card { padding: 28px 22px; }
  .feature { padding: 30px 24px; }
  .footer-grid { grid-template-columns: 1fr; gap: 28px; }
  .footer-bottom { flex-direction: column; align-items: flex-start; gap: 8px; }
  .contact-inner { padding: 10px 4px; }
}