:root {
  --bg: #f7f8fa;
  --surface: #ffffff;
  --text: #1f2430;
  --text-muted: #5b6472;
  --primary: #2b5ce6;
  --primary-dark: #1f4ac7;
  --accent: #0f9d8f;
  --border: #e6e8ee;
  --shadow: 0 6px 24px rgba(31, 36, 48, .08);
  --maxw: 1080px;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  margin-left: 240px; /* 为左侧导航留出空间 */
  transition: margin-left .3s ease;
}

a { color: var(--primary); text-decoration: none; }
img { max-width: 100%; display: block; }
.container { max-width: var(--maxw); margin: 0 auto; padding: 0 24px; }

/* ---------- 左侧导航栏 ---------- */
nav {
  position: fixed; top: 0; left: 0; bottom: 0; z-index: 100;
  width: 240px;
  background: var(--surface);
  border-right: 1px solid var(--border);
  transition: transform .3s ease;
}
nav .inner {
  height: 100%; padding: 32px 20px;
  display: flex; flex-direction: column; align-items: stretch;
  overflow-y: auto; scrollbar-width: thin; scrollbar-color: var(--border) transparent;
}
nav .inner::-webkit-scrollbar { width: 6px; }
nav .inner::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
.nav-head { display: flex; align-items: center; justify-content: space-between; }
.logo { font-weight: 700; font-size: 1.15rem; color: var(--text); }
.logo span { color: var(--primary); }
.nav-tag {
  margin-top: 4px; font-size: .72rem; color: var(--text-muted);
  letter-spacing: 1px;
}
.nav-links { list-style: none; display: flex; flex-direction: column; gap: 4px; margin-top: 36px; }
.nav-links a {
  display: block; padding: 11px 14px; border-radius: 10px;
  color: var(--text-muted); font-size: .95rem; transition: all .2s;
}
.nav-links a:hover { color: var(--primary); background: #eef1ff; }
.nav-sublinks {
  list-style: none; margin: 2px 0 8px 14px; padding-left: 12px;
  border-left: 1px solid var(--border);
}
.nav-sublinks a {
  display: block; padding: 6px 12px; border-radius: 8px;
  font-size: .85rem; color: var(--text-muted); transition: all .2s;
}
.nav-sublinks a:hover { color: var(--primary); background: #f0f3ff; }

/* 侧边栏可折叠分组 */
.nav-group > .nav-sublinks { display: none; }
.nav-group.open > .nav-sublinks { display: block; }
.nav-group-head { display: flex; align-items: center; gap: 4px; }
.nav-group-head > a { flex: 1; }
.nav-group-toggle {
  background: none; border: none; cursor: pointer; flex-shrink: 0;
  color: var(--text-muted); font-size: .75rem; padding: 10px 10px;
  border-radius: 8px; line-height: 1; transition: all .2s;
}
.nav-group-toggle:hover { color: var(--primary); background: var(--bg); }
.nav-group.open > .nav-group-head .nav-group-toggle { transform: rotate(90deg); }

/* 侧边栏整体收起/展开 */
.nav-foot { margin-top: auto; padding-top: 16px; border-top: 1px solid var(--border); }
.sidebar-collapse {
  display: none; width: 100%; padding: 10px; border: none; background: none; cursor: pointer;
  color: var(--text-muted); border-radius: 8px; font-size: .88rem;
  align-items: center; justify-content: center; gap: 6px; transition: all .2s;
}
.sidebar-collapse:hover { color: var(--primary); background: var(--bg); }
.sidebar-open {
  display: none; align-items: center; justify-content: center;
  position: fixed; top: 14px; left: 14px; z-index: 110;
  width: 44px; height: 44px; border-radius: 12px;
  background: var(--surface); border: 1px solid var(--border);
  font-size: 1.1rem; color: var(--text); box-shadow: var(--shadow); cursor: pointer;
}
@media (min-width: 769px) {
  .sidebar-collapse { display: flex; }
  body.nav-collapsed .sidebar-open { display: flex; }
  body.nav-collapsed { margin-left: 0; }
  body.nav-collapsed nav { transform: translateX(-100%); }
}

/* 桌面端隐藏:汉堡按钮 / 关闭按钮 / 遮罩层(移动端用) */
.hamburger, .nav-close { display: none; background: none; border: none; cursor: pointer; }
.overlay { display: none; position: fixed; inset: 0; z-index: 95; background: rgba(0,0,0,.35); }
.overlay.show { display: block; }

/* ---------- Hero ---------- */
header.hero {
  padding: 90px 0 70px;
  text-align: center;
}
.avatar {
  width: 110px; height: 110px; margin: 0 auto 24px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  display: flex; align-items: center; justify-content: center;
  color: #fff; font-size: 2.6rem; font-weight: 700;
  box-shadow: var(--shadow);
}
.hero h1 { font-size: 2.6rem; letter-spacing: .5px; }
.hero .subtitle { margin-top: 12px; font-size: 1.2rem; color: var(--text-muted); }
.hero .intro { max-width: 660px; margin: 20px auto 0; color: var(--text-muted); }
.hero-actions { margin-top: 32px; display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }
.btn {
  display: inline-block; padding: 12px 28px; border-radius: 999px;
  font-size: .98rem; font-weight: 600; transition: all .2s; cursor: pointer;
  border: 1px solid transparent;
}
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); }
.btn-ghost { background: transparent; color: var(--text); border-color: var(--border); }
.btn-ghost:hover { border-color: var(--primary); color: var(--primary); }

/* ---------- 通用区块 ---------- */
section { padding: 80px 0; }
.section-title {
  text-align: center; font-size: 1.9rem; margin-bottom: 14px; font-weight: 700;
}
.section-sub {
  text-align: center; color: var(--text-muted); max-width: 560px;
  margin: 0 auto 48px; font-size: .98rem;
}

/* ---------- 小板块标题(课程建议内) ---------- */
.sub-title {
  text-align: center; font-size: 1.35rem; font-weight: 700;
  margin: 56px 0 8px; letter-spacing: .5px;
}
.sub-title:first-of-type { margin-top: 0; }
.sub-title .num { color: var(--primary); margin-right: 8px; }
.sub-sub {
  text-align: center; color: var(--text-muted); max-width: 560px;
  margin: 0 auto 36px; font-size: .95rem;
}

/* ---------- 正文:副标题 + 内容 ---------- */
.plain-text { max-width: 800px; margin: 0 auto; }
.plain-text h4 {
  display: flex; align-items: center; gap: 8px;
  font-size: 1.05rem; font-weight: 700; margin: 22px 0 4px;
}
.plain-text h4::before {
  content: ""; width: 4px; height: 1em; border-radius: 2px;
  background: var(--primary); flex-shrink: 0;
}
.plain-text h4:first-child { margin-top: 0; }
.plain-text p { margin-bottom: 16px; font-size: .97rem; line-height: 1.9; color: var(--text); }

/* ---------- 页脚 ---------- */
footer { padding: 32px 0; text-align: center; color: var(--text-muted); font-size: .88rem; border-top: 1px solid var(--border); background: var(--surface); }

/* ---------- 响应式 ---------- */
@media (max-width: 768px) {
  body { margin-left: 0; }

  /* 抽屉式侧边导航 */
  nav {
    width: 260px; transform: translateX(-100%);
    transition: transform .3s ease;
  }
  nav.open { transform: translateX(0); box-shadow: 6px 0 24px rgba(0,0,0,.12); }
  .nav-links { margin-top: 24px; }

  /* 悬浮的打开按钮 */
  .hamburger {
    display: flex; align-items: center; justify-content: center;
    position: fixed; top: 14px; left: 14px; z-index: 110;
    width: 44px; height: 44px; border-radius: 12px;
    background: var(--surface); border: 1px solid var(--border);
    font-size: 1.3rem; color: var(--text); box-shadow: var(--shadow);
  }
  /* 侧边栏内的关闭按钮 */
  .nav-close {
    display: flex; align-items: center; justify-content: center;
    width: 36px; height: 36px; border-radius: 8px;
    font-size: 1rem; color: var(--text-muted);
  }
  .nav-close:hover { color: var(--text); background: var(--bg); }

  header.hero { padding: 100px 0 60px; }
  .hero h1 { font-size: 2rem; }
  .section-title { font-size: 1.6rem; }
}

/* ================= 多页面拆分后新增样式 ================= */

/* 子页面页头 */
.page-hero { padding: 64px 0 30px; text-align: center; }
.page-hero h1 { font-size: 2.1rem; letter-spacing: .5px; }
.page-hero .subtitle { margin-top: 10px; font-size: 1.08rem; color: var(--text-muted); }

/* 子页面正文间距 */
main section { padding: 40px 0 64px; }

/* 卡片网格(板块导航 / 科目概览 / 课程建议) */
.cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
  max-width: 900px;
  margin: 0 auto;
}
.card {
  display: block;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 24px;
  box-shadow: var(--shadow);
  transition: transform .25s, box-shadow .25s, border-color .25s;
}
.card:hover {
  transform: translateY(-4px);
  border-color: var(--primary);
  box-shadow: 0 10px 28px rgba(31, 36, 48, .14);
}
.card h3 {
  font-size: 1.08rem;
  margin-bottom: 8px;
  color: var(--text);
}
.card p {
  font-size: .92rem;
  color: var(--text-muted);
  margin: 0;
}

/* 编辑人列表(名字 + 头像) */
.editors {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  margin-top: 18px;
}
.editor {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 16px 10px 10px;
  color: var(--text);
  transition: all .2s;
}
.editor:hover { border-color: var(--primary); box-shadow: var(--shadow); }
.editor img { width: 44px; height: 44px; border-radius: 50%; }
.editor span { font-size: .92rem; font-weight: 600; }

@media (max-width: 768px) {
  .page-hero { padding: 96px 0 24px; }
  .page-hero h1 { font-size: 1.7rem; }
}