/* ==========================================================================
   大学物理下册 · 期中复习互动讲义
   主样式表
   ========================================================================== */

/* ---------- 1. 设计令牌 ---------- */
:root {
  --bg:            #f6f7fb;
  --bg-elev:       #ffffff;
  --bg-sunken:     #eef0f6;
  --bg-code:       #f2f4f9;
  --sidebar-bg:    #1b2130;
  --sidebar-fg:    #b9c1d4;
  --sidebar-active:#ffffff;
  --sidebar-hover: #262e42;

  --fg:            #1c2233;
  --fg-soft:       #4a5568;
  --fg-mute:       #7b8698;
  --border:        #e0e4ed;
  --border-strong: #cbd2e0;

  --accent:        #3b6ef6;
  --accent-soft:   #e8efff;
  --accent-fg:     #ffffff;

  --key:           #e8890c;   /* 重点 */
  --key-soft:      #fff5e4;
  --key-border:    #f3cf94;

  --trap:          #d92d3c;   /* 易错 */
  --trap-soft:     #fdeced;
  --trap-border:   #f3b4ba;

  --ok:            #12925c;
  --ok-soft:       #e6f6ee;

  --info:          #7a3ec9;
  --info-soft:     #f3ecfc;

  --shadow-sm: 0 1px 2px rgba(20, 28, 48, .06);
  --shadow-md: 0 4px 16px rgba(20, 28, 48, .08);
  --shadow-lg: 0 12px 40px rgba(20, 28, 48, .14);

  --radius:    12px;
  --radius-sm: 8px;
  --radius-lg: 18px;

  --sidebar-w: 288px;
  --font-cn: "PingFang SC", "Microsoft YaHei", "Hiragino Sans GB", "Source Han Sans SC",
             "Noto Sans CJK SC", "Source Han Sans CN", sans-serif;
  --font-math: "Cambria Math", "Latin Modern Math", "STIX Two Math", "Times New Roman", serif;
}

html[data-theme="dark"] {
  --bg:            #12151d;
  --bg-elev:       #1a1e29;
  --bg-sunken:     #0e1119;
  --bg-code:       #141822;
  --sidebar-bg:    #0c0f16;
  --sidebar-fg:    #9aa4bb;
  --sidebar-active:#ffffff;
  --sidebar-hover: #171c28;

  --fg:            #e4e8f2;
  --fg-soft:       #b3bcd0;
  --fg-mute:       #7d8799;
  --border:        #272d3c;
  --border-strong: #39415a;

  --accent:        #5b87ff;
  --accent-soft:   #1b2540;
  --accent-fg:     #0d1220;

  --key:           #f0a445;
  --key-soft:      #33280f;
  --key-border:    #5c4718;

  --trap:          #ff6b78;
  --trap-soft:     #351a1e;
  --trap-border:   #5e2b32;

  --ok:            #34c48d;
  --ok-soft:       #102c22;

  --info:          #a97cf0;
  --info-soft:     #241a38;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .4);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, .45);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, .6);
}

/* ---------- 2. 基础 ---------- */
*, *::before, *::after { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--font-cn);
  font-size: 16px;
  line-height: 1.85;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

::selection { background: var(--accent-soft); color: var(--fg); }

button, input, select, textarea { font-family: inherit; font-size: inherit; }

.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0;
}

/* 滚动条 */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 6px; border: 2px solid var(--bg); }
::-webkit-scrollbar-thumb:hover { background: var(--fg-mute); }

/* ---------- 3. 布局 ---------- */
.app {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr);
  min-height: 100vh;
}

/* ---------- 4. 侧边栏 ---------- */
.sidebar {
  background: var(--sidebar-bg);
  color: var(--sidebar-fg);
  display: flex;
  flex-direction: column;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow: hidden;
  z-index: 40;
}

.sidebar__head {
  padding: 20px 20px 16px;
  border-bottom: 1px solid rgba(255, 255, 255, .07);
  flex-shrink: 0;
}

.sidebar__title {
  display: flex; align-items: center; gap: 10px;
  font-size: 17px; font-weight: 700; color: #fff; letter-spacing: .3px;
  margin: 0 0 4px;
}
.sidebar__title .logo {
  width: 32px; height: 32px; border-radius: 9px; flex-shrink: 0;
  background: linear-gradient(135deg, #4f7cff, #7b5cff);
  display: grid; place-items: center; font-size: 17px;
  box-shadow: 0 3px 10px rgba(79, 124, 255, .35);
}
.sidebar__sub { font-size: 12.5px; color: #7f8aa3; line-height: 1.6; margin: 0; }

.sidebar__search {
  margin-top: 14px; position: relative;
}
.sidebar__search input {
  width: 100%; padding: 9px 12px 9px 34px;
  background: rgba(255, 255, 255, .06);
  border: 1px solid rgba(255, 255, 255, .1);
  border-radius: 9px; color: #fff; font-size: 13.5px; outline: none;
  transition: border-color .16s, background .16s;
}
.sidebar__search input::placeholder { color: #6b7691; }
.sidebar__search input:focus {
  border-color: rgba(120, 160, 255, .6); background: rgba(255, 255, 255, .09);
}
.sidebar__search .ico {
  position: absolute; left: 11px; top: 50%; transform: translateY(-50%);
  color: #6b7691; font-size: 13px; pointer-events: none;
}

.sidebar__nav {
  flex: 1; overflow-y: auto; padding: 12px 10px 24px;
  scrollbar-width: thin; scrollbar-color: rgba(255,255,255,.16) transparent;
}
.sidebar__nav::-webkit-scrollbar { width: 7px; }
.sidebar__nav::-webkit-scrollbar-thumb { background: rgba(255,255,255,.14); border: none; border-radius: 4px; }

.nav-group { margin-bottom: 6px; }
.nav-group__label {
  font-size: 11px; font-weight: 700; letter-spacing: 1.4px; text-transform: uppercase;
  color: #5e6a84; padding: 12px 12px 6px; user-select: none;
}
.nav-item {
  display: flex; align-items: center; gap: 9px;
  padding: 8px 12px; border-radius: 8px; margin-bottom: 1px;
  color: var(--sidebar-fg); font-size: 14px; line-height: 1.5;
  cursor: pointer; border: none; background: none; width: 100%; text-align: left;
  transition: background .13s, color .13s;
  position: relative;
}
.nav-item:hover { background: var(--sidebar-hover); color: #dfe5f2; text-decoration: none; }
.nav-item.is-active { background: var(--accent); color: #fff; font-weight: 600; }
.nav-item.is-active .nav-item__no { background: rgba(255,255,255,.22); color: #fff; }
.nav-item__no {
  font-size: 11px; font-weight: 700; min-width: 34px; height: 20px;
  display: grid; place-items: center; padding: 0 5px; border-radius: 5px;
  background: rgba(255, 255, 255, .07); color: #8b96b0; flex-shrink: 0;
}
.nav-item__label { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.nav-item__dot {
  width: 7px; height: 7px; border-radius: 50%; background: var(--ok);
  flex-shrink: 0; opacity: 0; transition: opacity .18s;
}
.nav-item.is-done .nav-item__dot { opacity: 1; }

.nav-item--tool { font-weight: 600; }
.nav-item--tool .nav-item__no { background: rgba(120,160,255,.16); color: #93b0ff; }
.nav-item--tool.is-active .nav-item__no { background: rgba(255,255,255,.22); color: #fff; }

/* 进度条 */
.sidebar__progress {
  padding: 12px 20px 16px; border-top: 1px solid rgba(255,255,255,.07);
  flex-shrink: 0;
}
.sidebar__progress .row {
  display: flex; justify-content: space-between; align-items: baseline;
  font-size: 12px; color: #7f8aa3; margin-bottom: 7px;
}
.sidebar__progress .row b { color: #fff; font-size: 15px; font-weight: 700; }
.pbar { height: 6px; border-radius: 4px; background: rgba(255,255,255,.09); overflow: hidden; }
.pbar__fill {
  height: 100%; border-radius: 4px;
  background: linear-gradient(90deg, #4f7cff, #34c48d);
  transition: width .45s cubic-bezier(.4, 0, .2, 1);
}

/* ---------- 5. 主区域 ---------- */
.main { min-width: 0; display: flex; flex-direction: column; }

.topbar {
  position: sticky; top: 0; z-index: 30;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
  padding: 0 32px; height: 58px;
  display: flex; align-items: center; gap: 16px;
}
.topbar__crumb {
  font-size: 13.5px; color: var(--fg-mute); flex: 1;
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.topbar__crumb b { color: var(--fg); font-weight: 600; }
.topbar__actions { display: flex; gap: 8px; align-items: center; }

.icon-btn {
  width: 34px; height: 34px; border-radius: 8px; border: 1px solid var(--border);
  background: var(--bg-elev); color: var(--fg-soft); cursor: pointer;
  display: grid; place-items: center; font-size: 15px;
  transition: all .15s;
}
.icon-btn:hover { border-color: var(--accent); color: var(--accent); }
.menu-btn { display: none; }

.content {
  padding: 30px 32px 90px;
  max-width: 1180px; width: 100%; margin: 0 auto;
}

/* ---------- 6. 页面标题 ---------- */
.page-head { margin-bottom: 26px; }
.page-head__eyebrow {
  display: inline-flex; align-items: center; gap: 7px;
  font-size: 12.5px; font-weight: 600; color: var(--accent);
  background: var(--accent-soft); padding: 4px 11px; border-radius: 20px;
  margin-bottom: 12px;
}
.page-head h1 {
  font-size: 30px; line-height: 1.35; margin: 0 0 10px; font-weight: 800;
  letter-spacing: -.3px;
}
.page-head__lead {
  font-size: 15.5px; color: var(--fg-soft); margin: 0; max-width: 76ch; line-height: 1.85;
}

/* ---------- 7. 卡片 / 分节 ---------- */
.section { margin-bottom: 26px; scroll-margin-top: 76px; }

.card {
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); box-shadow: var(--shadow-sm);
  overflow: hidden;
}

.card__head {
  display: flex; align-items: center; gap: 10px;
  padding: 15px 20px; border-bottom: 1px solid var(--border);
  background: linear-gradient(180deg, var(--bg-elev), var(--bg-sunken));
}
.card__icon {
  width: 28px; height: 28px; border-radius: 8px; display: grid; place-items: center;
  background: var(--accent-soft); color: var(--accent); font-size: 14px; flex-shrink: 0;
}
.card__title { font-size: 16.5px; font-weight: 700; margin: 0; flex: 1; letter-spacing: -.1px; }
.card__body { padding: 18px 20px 20px; }
.card__body > *:first-child { margin-top: 0; }
.card__body > *:last-child { margin-bottom: 0; }

.card--key .card__head { background: var(--key-soft); border-bottom-color: var(--key-border); }
.card--key .card__icon { background: var(--key); color: #fff; }
.card--key .card__title { color: var(--key); }

.card--trap .card__head { background: var(--trap-soft); border-bottom-color: var(--trap-border); }
.card--trap .card__icon { background: var(--trap); color: #fff; }
.card--trap .card__title { color: var(--trap); }

.card--formula { border-color: var(--border-strong); }
.card--formula .card__body { background: var(--bg-code); }

.card--compare .card__body { padding: 0; }

/* ---------- 8. 排版元素 ---------- */
.prose p { margin: 0 0 12px; }
.prose strong { color: var(--fg); font-weight: 700; }
.prose em { font-style: normal; color: var(--accent); font-weight: 600; }

.prose h4 {
  font-size: 14.5px; font-weight: 700; margin: 20px 0 10px;
  padding-left: 10px; border-left: 3px solid var(--accent); line-height: 1.5;
}
.prose h5 { font-size: 14px; font-weight: 700; margin: 16px 0 8px; color: var(--fg-soft); }

.prose ul, .prose ol { margin: 0 0 12px; padding-left: 22px; }
.prose li { margin-bottom: 6px; }
.prose li::marker { color: var(--fg-mute); }

.prose ul.bullets { list-style: none; padding-left: 0; }
.prose ul.bullets li {
  position: relative; padding-left: 22px; margin-bottom: 8px;
}
.prose ul.bullets li::before {
  content: ""; position: absolute; left: 6px; top: .78em;
  width: 6px; height: 6px; border-radius: 50%; background: var(--accent);
}

.prose ol.steps { list-style: none; counter-reset: st; padding-left: 0; }
.prose ol.steps li {
  counter-increment: st; position: relative; padding-left: 34px; margin-bottom: 10px;
}
.prose ol.steps li::before {
  content: counter(st); position: absolute; left: 0; top: .28em;
  width: 22px; height: 22px; border-radius: 50%;
  background: var(--accent); color: #fff; font-size: 12px; font-weight: 700;
  display: grid; place-items: center;
}

.callout {
  border-left: 3px solid var(--accent); background: var(--accent-soft);
  padding: 11px 15px; border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin: 0 0 14px; font-size: 14.5px; color: var(--fg-soft);
}
.callout--key { border-left-color: var(--key); background: var(--key-soft); }
.callout--trap { border-left-color: var(--trap); background: var(--trap-soft); }
.callout--ok { border-left-color: var(--ok); background: var(--ok-soft); }
.callout--info { border-left-color: var(--info); background: var(--info-soft); }
.callout p:last-child { margin-bottom: 0; }

/* 要点 / 易错 区块 */
.kv-block { margin-top: 16px; }
.kv-block__label {
  display: inline-flex; align-items: center; gap: 6px;
  font-size: 12.5px; font-weight: 700; letter-spacing: .4px;
  padding: 4px 11px; border-radius: 20px; margin-bottom: 10px;
}
.kv-block--points .kv-block__label { background: var(--key-soft); color: var(--key); }
.kv-block--traps .kv-block__label { background: var(--trap-soft); color: var(--trap); }
.kv-block ul { list-style: none; padding: 0; margin: 0; }
.kv-block li {
  position: relative; padding: 8px 12px 8px 32px; margin-bottom: 6px;
  background: var(--bg-sunken); border-radius: var(--radius-sm); font-size: 14.5px;
  line-height: 1.75;
}
.kv-block--points li::before {
  content: "★"; position: absolute; left: 11px; top: 8px; color: var(--key); font-size: 12px;
}
.kv-block--traps li::before {
  content: "✕"; position: absolute; left: 12px; top: 9px; color: var(--trap);
  font-size: 11px; font-weight: 700;
}
.kv-block--traps li { background: var(--trap-soft); }
.kv-block--points li { background: var(--key-soft); }

/* ---------- 9. 表格 ---------- */
.table-wrap {
  overflow-x: auto; margin: 0 0 16px;
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  background: var(--bg-elev);
}
.table-wrap table { border-collapse: collapse; width: 100%; font-size: 14px; }
.table-wrap th {
  background: var(--bg-sunken); font-weight: 700; text-align: left;
  padding: 11px 14px; border-bottom: 2px solid var(--border-strong);
  white-space: nowrap; font-size: 13.5px; color: var(--fg);
  position: sticky; top: 0;
}
.table-wrap td {
  padding: 11px 14px; border-bottom: 1px solid var(--border);
  vertical-align: top; line-height: 1.7;
}
.table-wrap tr:last-child td { border-bottom: none; }
.table-wrap tbody tr:hover { background: var(--bg-sunken); }
.table-wrap td:first-child { font-weight: 600; white-space: nowrap; }
.table-wrap .cell-math { min-width: 180px; }

/* ---------- 10. 数学渲染 ---------- */
.math-inline, .math-display { font-family: var(--font-math); }
.math-inline {
  display: inline; white-space: nowrap;
  color: var(--fg);
  font-size: 1.03em;
}
.math-display {
  display: block; text-align: center; margin: 16px 0;
  font-size: 1.14em; color: var(--fg);
  overflow-x: auto; overflow-y: hidden; padding: 4px 0;
}
.math-display .math-inline { display: inline; }

/* 分式：vertical-align: middle 让横线落在数学轴（基线上方约 .25em），
   避免 inline-flex 取“分子基线”导致整叠下坠 */
.m-frac {
  display: inline-flex; flex-direction: column; align-items: center;
  vertical-align: middle; margin: 0 .18em; line-height: 1.12;
  font-size: .9em;
}
.m-num { padding: 0 .28em; border-bottom: 1.4px solid currentColor; }
.m-den { padding: 0 .28em; }

/* 根号：容器用 inline-block（基线=根号内基线），√ 画在 .m-rad-body 的
   ::before 上，正好从顶横线延伸到内容底部，不需要拉伸字形 */
.m-sqrt {
  display: inline-block; position: relative;
  padding-left: .56em; margin: 0 .14em 0 .04em;
}
.m-sqrt > .m-rad { display: none; }
.m-rad-body {
  display: inline-block; position: relative; line-height: 1.15;
  padding: .04em .1em 0 .06em; border-top: 1.4px solid currentColor;
}
.m-rad-body::before {
  content: ""; position: absolute; left: -.5em; top: -.02em; bottom: -.02em; width: .5em;
  border-left: 1.4px solid currentColor; border-bottom: 1.4px solid currentColor;
  transform: skewX(-17deg); transform-origin: 0 100%;
  pointer-events: none;
}
.m-sqrt-idx {
  position: absolute; left: 0; top: -.46em; font-size: .62em; line-height: 1;
}

.m-script { display: inline-block; position: relative; white-space: nowrap; }
.m-sup, .m-sub {
  display: inline-block; font-size: .68em; line-height: 1;
}
.m-sup { vertical-align: .58em; }
.m-sub { vertical-align: -.28em; }

/* 装饰符（\vec \hat 等）：字母保持自己的基线，符号绝对定位到字母上方，
   既不撑高行盒、也不会把字母顶下去；符号本身用 CSS 形状画，位置可精确控制 */
.m-acc { display: inline-block; position: relative; line-height: 1; }
.m-acc-b { display: inline-block; line-height: 1; }
.m-acc-m {
  position: absolute; left: 50%; bottom: .92em;
  line-height: 0; height: 0; white-space: nowrap; pointer-events: none;
  transform: translateX(-50%);
}
/* \vec：横线 + 箭头 */
.m-acc-vec .m-acc-m { width: .6em; bottom: .95em; border-top: 1.4px solid currentColor; }
.m-acc-vec .m-acc-m::after {
  content: ""; position: absolute; right: -.04em; top: -.11em;
  border-left: .19em solid currentColor;
  border-top: .1em solid transparent; border-bottom: .1em solid transparent;
}
/* \hat：旋转的方框取两条边 = “^” */
.m-acc-hat .m-acc-m { width: .2em; height: .2em; bottom: .78em;
  border-left: 1.4px solid currentColor; border-top: 1.4px solid currentColor;
  transform: translateX(-50%) rotate(45deg); }
/* \bar / \overline 走 .m-overline；\tilde \dot 仍用字形，略作抬升 */
.m-acc-tilde .m-acc-m { bottom: .78em; }
.m-acc-dot .m-acc-m { bottom: .7em; }
.m-acc-ddot .m-acc-m { bottom: .8em; }

.m-overline { border-top: 1.3px solid currentColor; padding-top: .05em; }
.m-underline { border-bottom: 1.3px solid currentColor; }
.m-boxed { border: 1.4px solid currentColor; border-radius: 4px; padding: .06em .3em; }

.mat-text { font-family: var(--font-cn); font-size: .92em; }
.mat-rm { font-family: var(--font-cn); font-style: normal; }
.mat-bf { font-weight: 700; }
.mat-it { font-style: italic; }
.mat-bb { font-family: var(--font-math); }
.mat-cal { font-family: var(--font-math); }
.mat-space { display: inline-block; }
.mat-err { color: var(--trap); font-family: monospace; font-size: .85em; }

/* ---------- 11. 首页 ---------- */
.hero {
  background: linear-gradient(135deg, #3b6ef6 0%, #6d4ef0 55%, #8b3fd6 100%);
  border-radius: var(--radius-lg); padding: 38px 40px; color: #fff;
  margin-bottom: 28px; position: relative; overflow: hidden;
  box-shadow: var(--shadow-md);
}
.hero::after {
  content: ""; position: absolute; right: -60px; top: -60px;
  width: 280px; height: 280px; border-radius: 50%;
  background: rgba(255, 255, 255, .08);
}
.hero::before {
  content: ""; position: absolute; right: 40px; bottom: -90px;
  width: 190px; height: 190px; border-radius: 50%;
  background: rgba(255, 255, 255, .06);
}
.hero h1 { margin: 0 0 10px; font-size: 30px; font-weight: 800; letter-spacing: -.4px; }
.hero p { margin: 0 0 20px; font-size: 15.5px; opacity: .93; max-width: 68ch; line-height: 1.85; }
.hero__tags { display: flex; flex-wrap: wrap; gap: 8px; }
.hero__tag {
  background: rgba(255, 255, 255, .17); border: 1px solid rgba(255, 255, 255, .22);
  padding: 4px 12px; border-radius: 20px; font-size: 13px; font-weight: 500;
}

.stat-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(168px, 1fr));
  gap: 14px; margin-bottom: 28px;
}
.stat {
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 16px 18px; box-shadow: var(--shadow-sm);
  display: flex; align-items: center; gap: 13px;
}
.stat__icon {
  width: 40px; height: 40px; border-radius: 11px; display: grid; place-items: center;
  font-size: 19px; flex-shrink: 0;
}
.stat__num { font-size: 22px; font-weight: 800; line-height: 1.15; letter-spacing: -.4px; }
.stat__label { font-size: 12.5px; color: var(--fg-mute); }

.grid-2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); gap: 16px; }

.tile {
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 20px; box-shadow: var(--shadow-sm);
  cursor: pointer; transition: transform .16s, box-shadow .16s, border-color .16s;
  display: block; color: inherit; text-decoration: none;
}
.tile:hover {
  transform: translateY(-2px); box-shadow: var(--shadow-md); border-color: var(--accent);
  text-decoration: none;
}
.tile__icon {
  width: 38px; height: 38px; border-radius: 11px; display: grid; place-items: center;
  font-size: 18px; margin-bottom: 12px;
}
.tile h3 { margin: 0 0 6px; font-size: 16px; font-weight: 700; }
.tile p { margin: 0; font-size: 13.5px; color: var(--fg-mute); line-height: 1.7; }

/* 知识主线 */
.flow { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.flow__node {
  background: var(--bg-sunken); border: 1px solid var(--border);
  border-radius: 9px; padding: 7px 13px; font-size: 13.5px; font-weight: 600;
}
.flow__node--key { background: var(--key-soft); border-color: var(--key-border); color: var(--key); }
.flow__node--accent { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); }
.flow__arrow { color: var(--fg-mute); font-size: 14px; }

/* ---------- 12. 章节导航条 ---------- */
.chapnav {
  display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 22px;
  padding-bottom: 16px; border-bottom: 1px solid var(--border);
}
.chapnav__btn {
  border: 1px solid var(--border); background: var(--bg-elev); color: var(--fg-soft);
  padding: 6px 13px; border-radius: 8px; font-size: 13.5px; cursor: pointer;
  transition: all .15s;
}
.chapnav__btn:hover { border-color: var(--accent); color: var(--accent); }
.chapnav__btn.is-current {
  background: var(--accent); border-color: var(--accent); color: var(--accent-fg); font-weight: 600;
}

/* ---------- 13. 工具页 ---------- */
.tool-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 16px; }

.calc {
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow-sm);
}
.calc__head {
  padding: 14px 18px; border-bottom: 1px solid var(--border);
  background: linear-gradient(180deg, var(--bg-elev), var(--bg-sunken));
  display: flex; align-items: center; gap: 9px;
}
.calc__head h3 { margin: 0; font-size: 15.5px; font-weight: 700; flex: 1; }
.calc__body { padding: 16px 18px; }
.calc__body > *:last-child { margin-bottom: 0; }

.field { margin-bottom: 12px; }
.field label {
  display: block; font-size: 12.5px; font-weight: 600; color: var(--fg-soft); margin-bottom: 5px;
}
.field input, .field select {
  width: 100%; padding: 8px 11px; border: 1px solid var(--border-strong);
  border-radius: 8px; background: var(--bg); color: var(--fg); outline: none;
  font-size: 14px; transition: border-color .15s, box-shadow .15s;
}
.field input:focus, .field select:focus {
  border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft);
}
.field__unit { font-size: 12px; color: var(--fg-mute); font-weight: 500; }

.btn {
  padding: 9px 18px; border-radius: 9px; border: 1px solid var(--accent);
  background: var(--accent); color: var(--accent-fg); font-size: 14px; font-weight: 600;
  cursor: pointer; transition: filter .15s, transform .1s;
}
.btn:hover { filter: brightness(1.08); }
.btn:active { transform: scale(.98); }
.btn--ghost { background: transparent; color: var(--accent); }
.btn--ghost:hover { background: var(--accent-soft); }
.btn--sm { padding: 5px 12px; font-size: 13px; }
.btn:disabled { opacity: .5; cursor: not-allowed; }

.result {
  margin-top: 14px; padding: 14px 16px; border-radius: var(--radius-sm);
  background: var(--accent-soft); border: 1px solid var(--accent);
  font-size: 15px; line-height: 1.8;
}
.result__label {
  font-size: 12px; font-weight: 700; color: var(--accent);
  letter-spacing: .5px; margin-bottom: 6px;
}
.result__value { font-size: 19px; font-weight: 700; font-family: var(--font-math); }
.result__note { font-size: 12.5px; color: var(--fg-soft); margin-top: 6px; }

.preset-row { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 12px; }
.preset {
  border: 1px solid var(--border); background: var(--bg-sunken); color: var(--fg-soft);
  padding: 4px 10px; border-radius: 7px; font-size: 12.5px; cursor: pointer;
  transition: all .13s;
}
.preset:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }

/* ---------- 14. 测验 ---------- */
.quiz-shell { max-width: 860px; margin: 0 auto; }
.quiz-bar {
  display: flex; align-items: center; gap: 14px; margin-bottom: 18px;
  padding: 13px 18px; background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); box-shadow: var(--shadow-sm);
}
.quiz-bar__meta { flex: 1; font-size: 13.5px; color: var(--fg-soft); }
.quiz-bar__meta b { color: var(--fg); }
.quiz-bar .pbar { background: var(--bg-sunken); width: 150px; }
.quiz-bar .pbar__fill { background: linear-gradient(90deg, var(--accent), var(--ok)); }

.q-card {
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 26px 28px; box-shadow: var(--shadow-md);
  margin-bottom: 16px;
}
.q-card__top { display: flex; align-items: center; gap: 8px; margin-bottom: 14px; flex-wrap: wrap; }
.q-badge {
  font-size: 11.5px; font-weight: 700; padding: 3px 10px; border-radius: 20px;
  background: var(--bg-sunken); color: var(--fg-mute);
}
.q-badge--t { background: var(--accent-soft); color: var(--accent); }
.q-badge--d1 { background: var(--ok-soft); color: var(--ok); }
.q-badge--d2 { background: var(--key-soft); color: var(--key); }
.q-badge--d3 { background: var(--trap-soft); color: var(--trap); }
.q-card__stem { font-size: 16.5px; font-weight: 600; line-height: 1.8; margin-bottom: 18px; }

.q-options { display: flex; flex-direction: column; gap: 9px; margin-bottom: 16px; }
.q-opt {
  display: flex; gap: 12px; align-items: flex-start; padding: 12px 15px;
  border: 1.5px solid var(--border); border-radius: var(--radius-sm);
  cursor: pointer; transition: all .14s; background: var(--bg); font-size: 14.5px; line-height: 1.7;
}
.q-opt:hover { border-color: var(--accent); background: var(--accent-soft); }
.q-opt.is-picked { border-color: var(--accent); background: var(--accent-soft); }
.q-opt.is-right { border-color: var(--ok); background: var(--ok-soft); }
.q-opt.is-wrong { border-color: var(--trap); background: var(--trap-soft); }
.q-opt__key {
  width: 24px; height: 24px; border-radius: 50%; flex-shrink: 0;
  border: 1.5px solid var(--border-strong); display: grid; place-items: center;
  font-size: 12.5px; font-weight: 700; color: var(--fg-mute); background: var(--bg-elev);
  margin-top: 1px;
}
.q-opt.is-picked .q-opt__key { background: var(--accent); border-color: var(--accent); color: #fff; }
.q-opt.is-right .q-opt__key { background: var(--ok); border-color: var(--ok); color: #fff; }
.q-opt.is-wrong .q-opt__key { background: var(--trap); border-color: var(--trap); color: #fff; }
.q-opt__text { flex: 1; }

.q-feedback {
  border-radius: var(--radius-sm); padding: 15px 17px; font-size: 14.5px; line-height: 1.85;
  border: 1px solid; margin-bottom: 16px;
}
.q-feedback--right { background: var(--ok-soft); border-color: var(--ok); }
.q-feedback--wrong { background: var(--trap-soft); border-color: var(--trap); }
.q-feedback__title { font-weight: 700; margin-bottom: 6px; }
.q-feedback--right .q-feedback__title { color: var(--ok); }
.q-feedback--wrong .q-feedback__title { color: var(--trap); }

.q-actions { display: flex; gap: 10px; justify-content: flex-end; flex-wrap: wrap; }

.quiz-setup {
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 26px; box-shadow: var(--shadow-sm); max-width: 860px; margin: 0 auto;
}
.quiz-setup__row { margin-bottom: 18px; }
.quiz-setup__row > label {
  display: block; font-size: 13.5px; font-weight: 700; margin-bottom: 9px; color: var(--fg-soft);
}
.chip-row { display: flex; flex-wrap: wrap; gap: 8px; }
.chip {
  border: 1.5px solid var(--border); background: var(--bg); color: var(--fg-soft);
  padding: 6px 14px; border-radius: 20px; font-size: 13.5px; cursor: pointer;
  transition: all .13s;
}
.chip:hover { border-color: var(--accent); color: var(--accent); }
.chip.is-on { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); font-weight: 600; }

/* 结果页 */
.quiz-result { max-width: 700px; margin: 0 auto; text-align: center; }
.quiz-result__score {
  font-size: 62px; font-weight: 800; letter-spacing: -2px; line-height: 1.1;
  background: linear-gradient(135deg, var(--accent), #8b3fd6);
  -webkit-background-clip: text; background-clip: text; -webkit-text-fill-color: transparent;
}
.quiz-result__meta { color: var(--fg-mute); font-size: 14.5px; margin-bottom: 24px; }
.quiz-result__stats {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: 12px; margin-bottom: 24px; text-align: left;
}
.quiz-result__stat {
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 14px 16px;
}
.quiz-result__stat .n { font-size: 22px; font-weight: 800; }
.quiz-result__stat .l { font-size: 12.5px; color: var(--fg-mute); }

/* ---------- 15. 记忆卡 ---------- */
.deck-toolbar {
  display: flex; align-items: center; gap: 12px; margin-bottom: 20px; flex-wrap: wrap;
}
.deck-toolbar .spacer { flex: 1; }

.flashcard {
  perspective: 1400px; max-width: 720px; margin: 0 auto 18px;
}
.flashcard__inner {
  position: relative; width: 100%; min-height: 240px;
  transition: transform .5s cubic-bezier(.4, 0, .2, 1);
  transform-style: preserve-3d;
}
.flashcard.is-flipped .flashcard__inner { transform: rotateY(180deg); }
.flashcard__face {
  position: absolute; inset: 0; backface-visibility: hidden; -webkit-backface-visibility: hidden;
  background: var(--bg-elev); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 28px 30px; box-shadow: var(--shadow-md);
  display: flex; flex-direction: column; justify-content: center;
  overflow-y: auto;
}
.flashcard__face--back { transform: rotateY(180deg); background: var(--bg-code); }
.flashcard__label {
  font-size: 11.5px; font-weight: 700; letter-spacing: 1px; text-transform: uppercase;
  color: var(--fg-mute); margin-bottom: 12px;
}
.flashcard__q { font-size: 17px; font-weight: 600; line-height: 1.8; }
.flashcard__hint {
  margin-top: 18px; font-size: 12.5px; color: var(--fg-mute); text-align: center;
}
.flashcard__foot {
  display: flex; align-items: center; gap: 10px; margin-top: 20px;
  padding-top: 16px; border-top: 1px solid var(--border);
}
.flashcard__foot .spacer { flex: 1; }

.deck-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 12px; }
.deck-mini {
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 14px 16px; cursor: pointer; transition: all .15s;
}
.deck-mini:hover { border-color: var(--accent); transform: translateY(-1px); box-shadow: var(--shadow-sm); }
.deck-mini__q { font-size: 14px; font-weight: 600; line-height: 1.6; }
.deck-mini__t { font-size: 11.5px; color: var(--fg-mute); margin-top: 6px; }
.deck-mini.is-known { border-color: var(--ok); background: var(--ok-soft); }
.deck-mini.is-unknown { border-color: var(--trap); background: var(--trap-soft); }

/* ---------- 16. 搜索结果 ---------- */
.search-panel {
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 22px 24px; box-shadow: var(--shadow-sm);
}
.search-hit {
  padding: 13px 15px; border-radius: var(--radius-sm); border: 1px solid var(--border);
  margin-bottom: 9px; cursor: pointer; transition: all .14s; background: var(--bg);
}
.search-hit:hover { border-color: var(--accent); background: var(--accent-soft); }
.search-hit__title { font-size: 14.5px; font-weight: 700; margin-bottom: 3px; }
.search-hit__ctx { font-size: 13px; color: var(--fg-mute); line-height: 1.7; }
.search-hit mark { background: var(--key-soft); color: var(--key); padding: 0 2px; border-radius: 3px; font-weight: 700; }

/* ---------- 17. 自测清单 ---------- */
.checklist { list-style: none; padding: 0; margin: 0; }
.checklist li {
  display: flex; gap: 12px; align-items: flex-start; padding: 11px 14px;
  border: 1px solid var(--border); border-radius: var(--radius-sm); margin-bottom: 8px;
  background: var(--bg-elev); transition: all .14s; cursor: pointer;
}
.checklist li:hover { border-color: var(--accent); }
.checklist li.is-checked { background: var(--ok-soft); border-color: var(--ok); }
.checklist li.is-checked .checklist__q { text-decoration: line-through; opacity: .6; }
.checklist__box {
  width: 20px; height: 20px; border-radius: 6px; border: 1.5px solid var(--border-strong);
  flex-shrink: 0; display: grid; place-items: center; font-size: 12px; margin-top: 3px;
  color: transparent;
}
.checklist li.is-checked .checklist__box { background: var(--ok); border-color: var(--ok); color: #fff; }
.checklist__q { flex: 1; font-size: 14.5px; line-height: 1.75; }
.checklist__a {
  font-size: 13.5px; color: var(--fg-soft); margin-top: 5px;
  padding: 8px 12px; background: var(--bg-sunken); border-radius: 7px; line-height: 1.7;
}
.checklist li.is-checked .checklist__a { display: block; }

/* ---------- 18. 提示/空状态 ---------- */
.empty {
  text-align: center; padding: 60px 20px; color: var(--fg-mute);
}
.empty__icon { font-size: 44px; margin-bottom: 12px; }
.empty h3 { margin: 0 0 6px; color: var(--fg); font-size: 17px; }
.empty p { margin: 0; font-size: 14px; }

.toast {
  position: fixed; bottom: 26px; left: 50%; transform: translateX(-50%) translateY(20px);
  background: var(--fg); color: var(--bg); padding: 11px 20px; border-radius: 10px;
  font-size: 14px; font-weight: 600; box-shadow: var(--shadow-lg);
  opacity: 0; pointer-events: none; transition: all .28s; z-index: 100;
}
.toast.is-show { opacity: 1; transform: translateX(-50%) translateY(0); }

/* ---------- 19. 响应式 ---------- */
@media (max-width: 1000px) {
  .app { grid-template-columns: 1fr; }
  .sidebar {
    position: fixed; left: 0; top: 0; bottom: 0; width: var(--sidebar-w);
    transform: translateX(-100%); transition: transform .26s cubic-bezier(.4, 0, .2, 1);
    box-shadow: var(--shadow-lg);
  }
  .sidebar.is-open { transform: translateX(0); }
  .menu-btn { display: grid; }
  .content { padding: 22px 18px 80px; }
  .topbar { padding: 0 18px; }
  .hero { padding: 28px 24px; }
  .hero h1 { font-size: 24px; }
  .page-head h1 { font-size: 24px; }
}

@media (max-width: 620px) {
  body { font-size: 15.5px; }
  .q-card { padding: 20px 17px; }
  .flashcard__face { padding: 22px 20px; }
  .flashcard__inner { min-height: 280px; }
  .card__body { padding: 15px 16px; }
  .content { padding: 18px 13px 70px; }
  .hero { padding: 24px 19px; }
  .stat-grid { grid-template-columns: repeat(2, 1fr); }
}

/* 侧栏遮罩 */
.scrim {
  position: fixed; inset: 0; background: rgba(10, 14, 24, .5);
  z-index: 39; opacity: 0; pointer-events: none; transition: opacity .24s;
}
.scrim.is-show { opacity: 1; pointer-events: auto; }

@media print {
  .sidebar, .topbar, .chapnav, .scrim { display: none !important; }
  .app { grid-template-columns: 1fr; }
  .card { break-inside: avoid; box-shadow: none; }
  .content { padding: 0; max-width: none; }
}

/* ---------- 分段函数（\begin{cases}） ---------- */
.m-cases {
  display: inline-flex;
  flex-direction: column;
  vertical-align: middle;
  gap: 2px;
  margin: 0 .12em 0 .1em;
  padding-left: .5em;
  position: relative;
}
.m-cases::before {
  content: '{';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%) scaleY(2.4);
  font-size: 1.05em;
  line-height: 1;
  color: currentColor;
  opacity: .9;
}
.m-cases-row {
  display: flex;
  align-items: baseline;
  gap: .8em;
  white-space: nowrap;
}
.m-cases-val { text-align: right; }
.m-cases-cond { color: inherit; opacity: .82; font-size: .94em; }

/* ---------- 骨架类名兼容（index.html 实际使用的类名） ---------- */
.sidebar__brand {
  display: flex; align-items: center; gap: 11px; flex-shrink: 0;
  padding: 18px 20px 15px;
  border-bottom: 1px solid rgba(255, 255, 255, .07);
}
.sidebar__logo {
  width: 34px; height: 34px; border-radius: 10px; flex-shrink: 0;
  display: grid; place-items: center; font-size: 18px; line-height: 1;
  background: linear-gradient(135deg, #4f7cff, #7b5cff);
  box-shadow: 0 3px 10px rgba(79, 124, 255, .35);
}
.sidebar__brand .sidebar__title { font-size: 15px; margin: 0 0 2px; }
.sidebar__subtitle {
  font-size: 11.5px; color: #7f8aa3; line-height: 1.4;
  letter-spacing: .2px;
}
.sidebar__foot { margin-top: auto; flex-shrink: 0; }
.sidebar__progress-head {
  display: flex; justify-content: space-between; align-items: baseline;
  font-size: 12px; color: #7f8aa3; margin-bottom: 8px;
}
.sidebar__progress-head b { color: #fff; font-size: 14px; font-weight: 700; }
.sidebar__hint {
  padding: 0 20px 16px;
  font-size: 11px; line-height: 1.7; color: #5e6a84;
}

.topbar__icon {
  width: 36px; height: 36px; border-radius: 9px;
  border: 1px solid var(--border); background: var(--bg-elev);
  color: var(--fg-soft); font-size: 15px; line-height: 1;
  display: grid; place-items: center; cursor: pointer;
  transition: background .15s, border-color .15s, color .15s, transform .15s;
}
.topbar__icon:hover {
  background: var(--accent-soft); border-color: var(--accent);
  color: var(--accent); transform: translateY(-1px);
}
.topbar__icon:active { transform: translateY(0); }

.footer {
  margin-top: auto; padding: 26px 32px 30px;
  border-top: 1px solid var(--border);
  font-size: 12.5px; color: var(--fg-mute); line-height: 1.8;
}
.footer p { margin: 0 0 4px; }
.footer__dim { font-size: 11.5px; opacity: .8; }

.mat-sf { font-family: var(--font-cn); font-style: normal; }
.quiz-actions { display: flex; justify-content: flex-end; gap: 10px; }
.flashcard__face--front { background: var(--bg-elev); }

@media (max-width: 620px) {
  .footer { padding: 20px 18px 24px; }
  .sidebar__brand { padding: 15px 16px 13px; }
  .sidebar__hint { padding: 0 16px 14px; }
}