/* ===========================================================
   跟小佳老师学物理 —— 网站样式
   设计风格参考 jinxinlei.cn：学术个人站 + 卡片式资源导航
   配色：深蓝主色 + 青色点缀 + 暖橙强调，浅色背景
   =========================================================== */

:root {
  --primary: #1d4ed8;
  --primary-dark: #1e3a8a;
  --primary-light: #3b82f6;
  --accent: #06b6d4;
  --accent-warm: #f59e0b;
  --bg: #f5f8fc;
  --bg-soft: #eef3fb;
  --card: #ffffff;
  --text: #1f2937;
  --muted: #64748b;
  --border: #e5e9f0;
  --radius: 16px;
  --radius-sm: 10px;
  --shadow: 0 6px 24px rgba(29, 78, 216, 0.08);
  --shadow-hover: 0 12px 32px rgba(29, 78, 216, 0.16);
  --maxw: 1140px;
  --font: "PingFang SC", "Microsoft YaHei", "Hiragino Sans GB", "Source Han Sans CN", system-ui, -apple-system, sans-serif;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--primary); text-decoration: none; transition: color .2s; }
a:hover { color: var(--primary-light); }

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

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

/* ---------------- 顶部导航 ---------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 800;
  font-size: 19px;
  color: var(--primary-dark);
  letter-spacing: .5px;
}
.brand .logo-mark {
  width: 36px; height: 36px;
  border-radius: 10px;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  display: grid; place-items: center;
  color: #fff; font-size: 18px;
  box-shadow: 0 4px 12px rgba(29,78,216,.3);
}
.nav-links { display: flex; gap: 6px; align-items: center; }
.nav-links a {
  padding: 8px 14px;
  border-radius: 8px;
  color: var(--text);
  font-size: 15px;
  font-weight: 500;
}
.nav-links a:hover { background: var(--bg-soft); color: var(--primary); }
.nav-links a.active { background: var(--primary); color: #fff; }
.nav-cta {
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: #fff !important;
  padding: 8px 16px !important;
  border-radius: 999px !important;
  font-weight: 600;
  box-shadow: 0 4px 14px rgba(29,78,216,.3);
}
.nav-cta:hover { filter: brightness(1.05); }
.nav-toggle { display: none; background: none; border: none; font-size: 26px; cursor: pointer; color: var(--primary-dark); }

/* ---------------- Hero ---------------- */
.hero {
  position: relative;
  background: linear-gradient(135deg, #1e3a8a 0%, #1d4ed8 45%, #0891b2 100%);
  color: #fff;
  overflow: hidden;
  padding: 72px 0 88px;
}
.hero::after {
  content: "";
  position: absolute;
  right: -80px; top: -80px;
  width: 380px; height: 380px;
  background: radial-gradient(circle, rgba(255,255,255,.18), transparent 70%);
  border-radius: 50%;
}
.hero .container { position: relative; z-index: 2; }
.hero h1 { font-size: 44px; font-weight: 800; letter-spacing: 1px; margin-bottom: 14px; }
.hero .subtitle { font-size: 19px; opacity: .92; max-width: 640px; margin-bottom: 12px; }
.hero .tagline { font-size: 15px; opacity: .8; margin-bottom: 28px; }
.hero-btns { display: flex; gap: 14px; flex-wrap: wrap; }
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 24px; border-radius: 999px; font-weight: 600; font-size: 15px;
  cursor: pointer; border: none; transition: transform .15s, box-shadow .2s;
}
.btn-primary { background: #fff; color: var(--primary-dark); box-shadow: 0 6px 18px rgba(0,0,0,.15); }
.btn-primary:hover { transform: translateY(-2px); }
.btn-ghost { background: rgba(255,255,255,.14); color: #fff; border: 1px solid rgba(255,255,255,.4); }
.btn-ghost:hover { background: rgba(255,255,255,.24); }
.hero-orbit { position: absolute; right: 6%; top: 50%; transform: translateY(-50%); opacity: .9; }

/* ---------------- 通用 section ---------------- */
.section { padding: 64px 0; }
.section-alt { background: var(--bg-soft); }
.section-head { text-align: center; margin-bottom: 40px; }
.section-head .eyebrow { color: var(--accent); font-weight: 700; letter-spacing: 2px; font-size: 13px; text-transform: uppercase; }
.section-head h2 { font-size: 30px; font-weight: 800; color: var(--primary-dark); margin: 6px 0 8px; }
.section-head p { color: var(--muted); max-width: 640px; margin: 0 auto; }

/* ---------------- 卡片网格 ---------------- */
.grid { display: grid; gap: 22px; }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 26px 24px;
  box-shadow: var(--shadow);
  transition: transform .2s, box-shadow .2s, border-color .2s;
  display: flex; flex-direction: column;
}
.card:hover { transform: translateY(-4px); box-shadow: var(--shadow-hover); border-color: var(--primary-light); }
.card .icon {
  width: 52px; height: 52px; border-radius: 14px;
  display: grid; place-items: center; font-size: 26px; margin-bottom: 16px;
  background: linear-gradient(135deg, #dbeafe, #cffafe);
}
.card h3 { font-size: 19px; color: var(--primary-dark); margin-bottom: 8px; }
.card p { color: var(--muted); font-size: 14.5px; flex: 1; }
.card .more { margin-top: 16px; font-weight: 600; font-size: 14px; color: var(--primary); }

/* ---------------- 介绍 / 关于 ---------------- */
.intro-grid { display: grid; grid-template-columns: 1.4fr 1fr; gap: 40px; align-items: center; }
.intro-text h2 { font-size: 28px; color: var(--primary-dark); margin-bottom: 14px; }
.intro-text p { color: var(--muted); margin-bottom: 14px; }
.intro-text ul { list-style: none; margin: 14px 0; }
.intro-text li { padding: 8px 0 8px 28px; position: relative; color: var(--text); }
.intro-text li::before {
  content: "✦"; position: absolute; left: 0; top: 8px; color: var(--accent); font-weight: 700;
}
.intro-card {
  background: linear-gradient(160deg, #fff, #f0f7ff);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow);
  text-align: center;
}
.qr-box {
  width: 160px; height: 160px; margin: 10px auto 14px;
  border: 2px dashed var(--primary-light);
  border-radius: 12px;
  display: grid; place-items: center;
  color: var(--muted); font-size: 13px; text-align: center;
  background: #fafcff;
}
.intro-card h4 { color: var(--primary-dark); margin-bottom: 4px; }

/* ---------------- 列表 / 资源条目 ---------------- */
.resource-list { display: grid; gap: 14px; }
.resource-item {
  display: flex; align-items: center; gap: 16px;
  background: var(--card); border: 1px solid var(--border);
  border-radius: var(--radius-sm); padding: 16px 20px;
  transition: border-color .2s, box-shadow .2s;
}
.resource-item:hover { border-color: var(--primary-light); box-shadow: var(--shadow); }
.resource-item .badge {
  flex-shrink: 0; padding: 6px 12px; border-radius: 8px;
  font-size: 13px; font-weight: 700; color: #fff;
  background: linear-gradient(135deg, var(--primary), var(--accent));
}
.resource-item .meta { flex: 1; }
.resource-item .meta h4 { font-size: 16px; color: var(--text); margin-bottom: 2px; }
.resource-item .meta span { font-size: 13px; color: var(--muted); }
.resource-item .go { color: var(--primary); font-weight: 600; font-size: 14px; white-space: nowrap; }

/* ---------------- 标签页（年级切换） ---------------- */
.tabs { display: flex; gap: 10px; justify-content: center; flex-wrap: wrap; margin-bottom: 30px; }
.tab {
  padding: 9px 20px; border-radius: 999px; border: 1px solid var(--border);
  background: #fff; cursor: pointer; font-weight: 600; color: var(--muted); font-size: 14px;
}
.tab.active { background: var(--primary); color: #fff; border-color: var(--primary); }
.tab:hover:not(.active) { border-color: var(--primary-light); color: var(--primary); }
.tab-panel { display: none; }
.tab-panel.active { display: block; }

/* ---------------- 页脚 ---------------- */
.site-footer { background: #0f1f47; color: #cbd5e1; padding: 48px 0 24px; }
.footer-grid { display: grid; grid-template-columns: 1.6fr 1fr 1fr; gap: 36px; margin-bottom: 30px; }
.site-footer h4 { color: #fff; font-size: 16px; margin-bottom: 14px; }
.site-footer a { color: #cbd5e1; }
.site-footer a:hover { color: #fff; }
.site-footer p { font-size: 14px; line-height: 1.9; }
.footer-links li { list-style: none; padding: 5px 0; font-size: 14px; }
.footer-bottom {
  border-top: 1px solid rgba(255,255,255,.12);
  padding-top: 18px; text-align: center; font-size: 13px; color: #94a3b8;
}
.footer-bottom a { color: #94a3b8; }

/* ---------------- 提示横幅（部署占位） ---------------- */
.notice {
  background: #fffbeb; border: 1px solid #fde68a; color: #92400e;
  border-radius: var(--radius-sm); padding: 14px 18px; font-size: 14px; margin: 24px 0;
}

/* ---------------- 响应式 ---------------- */
@media (max-width: 920px) {
  .grid-3, .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .intro-grid { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 640px) {
  .hero h1 { font-size: 32px; }
  .hero .subtitle { font-size: 16px; }
  .hero-orbit { display: none; }
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; }
  .nav-links {
    position: absolute; top: 64px; left: 0; right: 0;
    background: #fff; flex-direction: column; align-items: stretch;
    padding: 10px; border-bottom: 1px solid var(--border);
    display: none;
  }
  .nav-links.open { display: flex; }
  .nav-toggle { display: block; }
}