/* ============================================================
 * THUSSAT Edu 官网 —— 全局样式（品牌视觉 v1）
 * 主色：#2E5BFF 品牌蓝；THU 辅诠释（Technology·Humanity·Understanding）
 * 设计：现代、留白、响应式、无障碍
 * ============================================================ */
:root {
  --primary: #2E5BFF;
  --primary-dark: #1f44c9;
  --primary-soft: #eef2ff;
  --ink: #1a2233;
  --muted: #6b7488;
  --bg: #ffffff;
  --bg-soft: #f6f8fd;
  --line: #e3e8f2;
  --grad: linear-gradient(160deg, #101a3c 0%, #1f2f6e 55%, #2E5BFF 130%);
  --radius: 16px;
  --shadow: 0 10px 40px rgba(20, 30, 80, .10);
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: "Inter", "Noto Sans SC", "Segoe UI", system-ui, sans-serif;
  color: var(--ink); background: var(--bg); line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
img { max-width: 100%; }
.container { max-width: 1120px; margin: 0 auto; padding: 0 24px; }

/* ---------- 顶栏 ---------- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255,255,255,.92); backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.header-inner { display: flex; align-items: center; gap: 28px; height: 72px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 800; font-size: 18px; letter-spacing: .02em; }
.brand img { height: 40px; width: auto; }
.brand .brand-sub { font-size: 12px; font-weight: 500; color: var(--muted); letter-spacing: .05em; }
.nav { display: flex; gap: 22px; margin-left: auto; align-items: center; }
.nav a { color: var(--ink); font-size: 15px; font-weight: 500; }
.nav a:hover { color: var(--primary); text-decoration: none; }
.lang-switch { display: flex; gap: 2px; border: 1px solid var(--line); border-radius: 10px; padding: 3px; }
.lang-btn {
  border: none; background: transparent; cursor: pointer;
  padding: 4px 12px; border-radius: 7px; font-size: 13px; font-weight: 600;
  color: var(--muted); font-family: inherit; transition: .15s;
}
.lang-btn:hover { color: var(--ink); }
.lang-btn.active { background: var(--primary); color: #fff; }

/* ---------- Hero ---------- */
.hero { background: var(--grad); color: #fff; padding: 96px 0 80px; position: relative; overflow: hidden; }
.hero::after {
  content: ""; position: absolute; inset: 0; pointer-events: none;
  background: radial-gradient(600px 300px at 85% 20%, rgba(255,255,255,.12), transparent 60%);
}
.hero-inner { position: relative; text-align: center; max-width: 760px; margin: 0 auto; }
.hero .hero-logo { height: 84px; width: auto; margin-bottom: 24px; filter: drop-shadow(0 4px 12px rgba(0,0,0,.2)); }
.hero h1 { font-size: 44px; font-weight: 800; letter-spacing: .01em; line-height: 1.2; }
.hero .hero-tag { margin-top: 18px; font-size: 20px; color: #cdd7ff; font-weight: 500; }
.hero .hero-sub { margin-top: 10px; font-size: 15px; color: #9fb0e8; letter-spacing: .08em; }
.hero .hero-cta { margin-top: 36px; display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 14px 30px; border-radius: 12px; font-size: 16px; font-weight: 700;
  cursor: pointer; border: none; transition: .18s; font-family: inherit;
}
.btn-primary { background: #fff; color: var(--primary-dark); }
.btn-primary:hover { background: #eef2ff; text-decoration: none; transform: translateY(-1px); }
.btn-ghost-light { background: transparent; color: #fff; border: 1.5px solid rgba(255,255,255,.5); }
.btn-ghost-light:hover { border-color: #fff; text-decoration: none; }
.btn-ghost { background: transparent; color: var(--primary); border: 1.5px solid var(--primary); }
.btn-ghost:hover { background: var(--primary-soft); text-decoration: none; }

/* ---------- 区块 ---------- */
.section { padding: 84px 0; }
.section.soft { background: var(--bg-soft); }
.section-head { text-align: center; max-width: 680px; margin: 0 auto 52px; }
.section-head .kicker { color: var(--primary); font-weight: 700; font-size: 14px; letter-spacing: .1em; text-transform: uppercase; }
.section-head h2 { font-size: 32px; font-weight: 800; margin-top: 10px; }
.section-head p { color: var(--muted); margin-top: 14px; font-size: 16px; }

/* THU 三支柱 */
.pillars { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.pillar {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 32px 26px; box-shadow: var(--shadow); transition: .2s;
}
.pillar:hover { transform: translateY(-4px); box-shadow: 0 18px 50px rgba(20,30,80,.14); }
.pillar .num {
  width: 40px; height: 40px; border-radius: 12px; background: var(--primary-soft);
  color: var(--primary); font-weight: 800; font-size: 18px;
  display: flex; align-items: center; justify-content: center; margin-bottom: 18px;
}
.pillar h3 { font-size: 20px; font-weight: 700; }
.pillar .en { color: var(--muted); font-size: 13px; letter-spacing: .04em; margin: 4px 0 12px; }
.pillar p { color: var(--muted); font-size: 15px; }

/* SSAT 四能力 */
.ssat { display: grid; grid-template-columns: repeat(4, 1fr); gap: 18px; }
.ssat-card {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 26px 22px; text-align: center;
}
.ssat-card .letter {
  width: 52px; height: 52px; margin: 0 auto 14px; border-radius: 14px;
  background: var(--grad); color: #fff; font-size: 26px; font-weight: 800;
  display: flex; align-items: center; justify-content: center;
}
.ssat-card h4 { font-size: 17px; font-weight: 700; }
.ssat-card .en { color: var(--muted); font-size: 12px; margin: 3px 0 8px; letter-spacing: .04em; }
.ssat-card p { color: var(--muted); font-size: 14px; }

/* 语录 */
.quote {
  background: var(--grad); color: #fff; text-align: center; padding: 72px 0;
}
.quote blockquote { font-size: 26px; font-weight: 700; max-width: 720px; margin: 0 auto; line-height: 1.5; }
.quote .by { margin-top: 16px; color: #cdd7ff; font-size: 15px; letter-spacing: .06em; }

/* 课程卡片 */
.course-cards { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.course-card {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 30px 26px; box-shadow: var(--shadow); display: flex; flex-direction: column; gap: 12px;
}
.course-card .part {
  align-self: flex-start; background: var(--primary-soft); color: var(--primary);
  font-size: 12px; font-weight: 700; padding: 4px 12px; border-radius: 20px; letter-spacing: .04em;
}
.course-card h3 { font-size: 20px; font-weight: 700; }
.course-card p { color: var(--muted); font-size: 15px; flex: 1; }
.course-card ul { list-style: none; display: flex; flex-direction: column; gap: 6px; }
.course-card li { font-size: 14px; color: var(--ink); }
.course-card li::before { content: "✓ "; color: var(--primary); font-weight: 700; }

/* 合作 */
.partner-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 24px; }
.partner {
  background: #fff; border: 1px solid var(--line); border-radius: var(--radius);
  padding: 30px 26px; box-shadow: var(--shadow);
}
.partner h3 { font-size: 19px; font-weight: 700; margin-bottom: 10px; }
.partner p { color: var(--muted); font-size: 15px; margin-bottom: 12px; }
.partner ul { list-style: none; display: flex; flex-direction: column; gap: 6px; }
.partner li { font-size: 14px; }
.partner li::before { content: "— "; color: var(--primary); font-weight: 700; }

/* 证书核验 */
.verify-wrap { max-width: 620px; margin: 0 auto; }
.verify-card {
  background: #fff; border: 1px solid var(--line); border-radius: 20px;
  padding: 40px 36px; box-shadow: var(--shadow);
}
.verify-card label { display: block; font-size: 14px; color: var(--muted); margin-bottom: 8px; font-weight: 600; }
.verify-card input {
  width: 100%; padding: 14px 16px; border: 1.5px solid var(--line); border-radius: 12px;
  font-size: 16px; font-family: inherit; outline: none; transition: .15s;
}
.verify-card input:focus { border-color: var(--primary); }
.verify-card .btn { width: 100%; margin-top: 16px; justify-content: center; }
.verify-result { margin-top: 20px; border-radius: 14px; padding: 22px; display: none; }
.verify-result.ok { display: block; background: #f0fdf4; border: 1px solid #bbf7d0; color: #166534; }
.verify-result.bad { display: block; background: #fef2f2; border: 1px solid #fecaca; color: #991b1b; }
.verify-result h4 { font-size: 17px; margin-bottom: 8px; }

/* 页脚 */
.site-footer { background: #101a3c; color: #9fb0e8; padding: 48px 0 40px; }
.footer-inner { display: flex; justify-content: space-between; gap: 32px; flex-wrap: wrap; }
.footer-brand img { height: 36px; width: auto; background: #fff; border-radius: 8px; padding: 4px 8px; margin-bottom: 12px; }
.footer-brand .name { color: #fff; font-weight: 700; font-size: 16px; }
.footer-brand .org { font-size: 13px; margin-top: 6px; }
.footer-links { display: flex; gap: 48px; }
.footer-links h5 { color: #fff; font-size: 14px; margin-bottom: 12px; }
.footer-links a { display: block; color: #9fb0e8; font-size: 14px; padding: 4px 0; }
.footer-links a:hover { color: #fff; text-decoration: none; }
.footer-bottom { text-align: center; margin-top: 36px; padding-top: 22px; border-top: 1px solid rgba(255,255,255,.1); font-size: 13px; }

@media (max-width: 900px) {
  .pillars, .course-cards, .partner-grid { grid-template-columns: 1fr; }
  .ssat { grid-template-columns: repeat(2, 1fr); }
  .hero h1 { font-size: 32px; }
  .nav { gap: 14px; }
  .nav a { font-size: 14px; }
}