:root {
  --bg: #f4f6fb;
  --card: #ffffff;
  --pri: #2563eb;
  --pri-dark: #1d4ed8;
  --pri-soft: #e8efff;
  --text: #1f2937;
  --muted: #6b7280;
  --line: #e5e7eb;
  --green: #16a34a;
  --green-soft: #e8f7ee;
  --red: #dc2626;
  --red-soft: #fdecec;
  --amber: #b45309;
  --amber-soft: #fff7e6;
  --radius: 16px;
  --shadow: 0 6px 20px rgba(17, 24, 39, .06);
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  font-size: 16px;
  line-height: 1.65;
}

body { padding-bottom: env(safe-area-inset-bottom); }

button { font-family: inherit; }

#app {
  max-width: 640px;
  margin: 0 auto;
  padding: 16px 16px calc(84px + env(safe-area-inset-bottom));
  min-height: 100vh;
}

/* 顶部品牌区 */
.hero {
  background: linear-gradient(135deg, #2563eb 0%, #4f46e5 100%);
  border-radius: 22px;
  padding: 20px 18px 16px;
  color: #fff;
  box-shadow: 0 10px 24px rgba(37, 99, 235, .25);
}
.hero-title { font-size: 22px; font-weight: 700; letter-spacing: .5px; }
.hero-sub { font-size: 13px; opacity: .85; margin-top: 2px; }
.hero-stats {
  display: flex;
  margin-top: 16px;
  background: rgba(255, 255, 255, .14);
  border-radius: 14px;
  padding: 10px 0;
}
.hero-stats > div { flex: 1; text-align: center; }
.hero-stats b { display: block; font-size: 20px; line-height: 1.2; }
.hero-stats span { font-size: 11px; opacity: .85; }

.section-title {
  font-size: 14px;
  font-weight: 600;
  color: var(--muted);
  margin: 22px 4px 10px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

/* 章节卡 */
.chapter {
  background: var(--card);
  border-radius: var(--radius);
  padding: 14px 16px;
  margin-bottom: 10px;
  box-shadow: var(--shadow);
}
.chapter-head { display: flex; align-items: baseline; gap: 8px; }
.ch-no { font-size: 12px; color: var(--pri); font-weight: 700; }
.ch-title { font-size: 16px; font-weight: 600; }
.ch-range { font-size: 12px; color: var(--muted); margin-top: 2px; }
.bar {
  height: 7px;
  background: #eef1f7;
  border-radius: 99px;
  overflow: hidden;
  margin: 10px 0 8px;
}
.bar > i {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, #3b82f6, #2563eb);
  border-radius: 99px;
  transition: width .3s ease;
}
.ch-foot {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  color: var(--muted);
}
.ch-foot > span { flex: 1; }

/* 按钮 */
.btn {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--text);
  border-radius: 10px;
  padding: 8px 14px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  transition: transform .08s ease, opacity .2s ease;
}
.btn:active { transform: scale(.97); }
.btn-sm { padding: 6px 12px; font-size: 13px; }
.btn-primary { background: var(--pri); border-color: var(--pri); color: #fff; }
.btn-primary:disabled { opacity: .45; }
.btn-ghost { background: transparent; }
.btn-block { display: block; width: 100%; padding: 12px; font-size: 15px; margin-top: 14px; }
.btn-danger { color: var(--red); border-color: #fecaca; background: #fff; }

/* 练习页顶栏 */
.topbar {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
}
.icon-btn {
  width: 38px;
  height: 38px;
  border-radius: 12px;
  border: 1px solid var(--line);
  background: #fff;
  font-size: 18px;
  line-height: 1;
  cursor: pointer;
  flex-shrink: 0;
}
.topbar-title { font-size: 16px; font-weight: 600; flex: 1; }
.topbar-sub { font-size: 13px; color: var(--muted); }

.progress-line {
  height: 5px;
  background: #e6ebf4;
  border-radius: 99px;
  overflow: hidden;
  margin-bottom: 14px;
}
.progress-line > i {
  display: block;
  height: 100%;
  background: var(--pri);
  border-radius: 99px;
  transition: width .25s ease;
}

/* 题目卡 */
.card {
  background: var(--card);
  border-radius: var(--radius);
  padding: 18px 16px;
  box-shadow: var(--shadow);
}
.q-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 10px;
  font-size: 11px;
  color: var(--muted);
}
.chip {
  background: #f1f4fa;
  border-radius: 99px;
  padding: 2px 9px;
  font-size: 11px;
  color: var(--muted);
}
.chip.pri { background: var(--pri-soft); color: var(--pri); }
.chip.warn { background: var(--amber-soft); color: var(--amber); }
.chip.stars {
  background: transparent;
  color: #f59e0b;
  letter-spacing: 1px;
  font-weight: 600;
  padding-left: 4px;
  padding-right: 4px;
}

.q-stem {
  font-size: 17px;
  line-height: 1.8;
  margin: 2px 0 16px;
  word-break: break-word;
}
.q-stem sub, .q-stem sup { font-size: 70%; }

/* 选项 */
.opts { display: flex; flex-direction: column; gap: 9px; }
.opt {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  text-align: left;
  border: 1.5px solid var(--line);
  background: #fff;
  border-radius: 12px;
  padding: 11px 12px;
  font-size: 15px;
  line-height: 1.55;
  color: var(--text);
  cursor: pointer;
}
.opt:active { background: #f8fafc; }
.opt-l {
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: #f1f4fa;
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  margin-top: 1px;
}
.opt.selected { border-color: var(--pri); background: var(--pri-soft); }
.opt.selected .opt-l { background: var(--pri); color: #fff; }
.opt.correct { border-color: var(--green); background: var(--green-soft); }
.opt.correct .opt-l { background: var(--green); color: #fff; }
.opt.wrong { border-color: var(--red); background: var(--red-soft); }
.opt.wrong .opt-l { background: var(--red); color: #fff; }
.opt:disabled { cursor: default; }

/* 填空 */
.fill {
  width: 100%;
  border: 1.5px solid var(--line);
  border-radius: 12px;
  padding: 12px 14px;
  font-size: 16px;
  outline: none;
  background: #fff;
  color: var(--text);
}
.fill:focus { border-color: var(--pri); box-shadow: 0 0 0 3px var(--pri-soft); }

.actions { display: flex; gap: 10px; margin-top: 14px; }
.actions .btn { flex: 1; }

/* 答案与解析 */
.answer-banner {
  margin-top: 16px;
  border-radius: 12px;
  padding: 10px 12px;
  font-size: 14px;
  font-weight: 600;
}
.answer-banner.ok { background: var(--green-soft); color: var(--green); }
.answer-banner.bad { background: var(--red-soft); color: var(--red); }
.answer-banner.info { background: var(--pri-soft); color: var(--pri); }

.sol { margin-top: 14px; }
.sol-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--muted);
  letter-spacing: 1px;
  margin-bottom: 6px;
}
.sol p {
  margin: 0 0 8px;
  font-size: 15px;
  line-height: 1.75;
  color: #374151;
}
.key-box {
  margin-top: 12px;
  background: var(--amber-soft);
  border-left: 3px solid #f59e0b;
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 14px;
  color: #78350f;
}
.key-box b { color: #b45309; margin-right: 4px; }
.pitfall-box {
  margin-top: 10px;
  background: #f8fafc;
  border-left: 3px solid #cbd5e1;
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 13.5px;
  color: #475569;
}
.pitfall-box b { color: #334155; margin-right: 4px; }

.judge { display: flex; gap: 10px; margin-top: 12px; }
.judge .btn { flex: 1; }
.judge .yes { border-color: #bbf7d0; color: var(--green); }
.judge .no { border-color: #fecaca; color: var(--red); }

/* 结果页 */
.result {
  text-align: center;
  padding: 26px 16px;
}
.result .big { font-size: 40px; font-weight: 800; color: var(--pri); line-height: 1.2; }
.result .sub { color: var(--muted); font-size: 14px; margin-top: 4px; }

/* 统计 */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-bottom: 14px;
}
.stat-card {
  background: var(--card);
  border-radius: 14px;
  padding: 12px 8px;
  text-align: center;
  box-shadow: var(--shadow);
}
.stat-card b { display: block; font-size: 20px; }
.stat-card span { font-size: 11px; color: var(--muted); }

.stat-row {
  background: var(--card);
  border-radius: 12px;
  padding: 12px 14px;
  margin-bottom: 8px;
  box-shadow: var(--shadow);
}
.stat-row .line1 { display: flex; justify-content: space-between; font-size: 14px; margin-bottom: 6px; }
.stat-row .line1 span:last-child { color: var(--muted); font-size: 12px; }

/* 错题本 */
.wrong-item {
  background: var(--card);
  border-radius: 14px;
  padding: 14px 16px;
  margin-bottom: 10px;
  box-shadow: var(--shadow);
}
.wrong-item .q-stem { font-size: 15px; margin: 8px 0 10px; }
.wrong-item .foot { display: flex; gap: 8px; }

.empty {
  text-align: center;
  color: var(--muted);
  font-size: 14px;
  padding: 38px 10px;
}
.empty .big { font-size: 34px; margin-bottom: 8px; }

/* 公式 */
.fml-search {
  width: 100%;
  box-sizing: border-box;
  border: 1px solid #dbe3ef;
  background: #fff;
  border-radius: 12px;
  padding: 11px 13px;
  font-size: 14px;
  color: var(--text);
  outline: none;
  margin: 2px 0 10px;
  -webkit-appearance: none;
}
.fml-search:focus { border-color: var(--pri); }
.fml-search::placeholder { color: #9aa7bd; }

.fml-nav {
  display: flex;
  gap: 6px;
  overflow-x: auto;
  padding: 0 0 12px;
  -webkit-overflow-scrolling: touch;
  scrollbar-width: none;
}
.fml-nav::-webkit-scrollbar { display: none; }
.fml-nav a {
  flex: 0 0 auto;
  font-size: 12px;
  line-height: 1;
  padding: 7px 10px;
  border-radius: 999px;
  background: #eef4ff;
  color: var(--pri);
  text-decoration: none;
}

.formula-group {
  margin-bottom: 18px;
  scroll-margin-top: 12px;
}
.formula-group h3 {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 7px;
  font-size: 15px;
  color: var(--pri);
  margin: 0 0 7px 2px;
}
.fg-sub {
  font-size: 11px;
  font-weight: 400;
  color: var(--muted);
}
.fg-tip {
  font-size: 12px;
  line-height: 1.65;
  color: #64748b;
  background: #f1f5f9;
  border-radius: 9px;
  padding: 7px 10px;
  margin: 0 0 8px;
}
.formula-item {
  display: flex;
  align-items: flex-start;
  gap: 9px;
  background: var(--card);
  border-radius: 10px;
  padding: 9px 11px 9px 8px;
  margin-bottom: 7px;
  box-shadow: var(--shadow);
}
.fi-no {
  flex: 0 0 20px;
  width: 20px;
  text-align: right;
  font-size: 11px;
  line-height: 1.9;
  color: #9aa7bd;
  font-variant-numeric: tabular-nums;
}
.fi-body { flex: 1 1 auto; min-width: 0; }
.formula-item .expr {
  font-size: 15.5px;
  line-height: 1.9;
  word-break: break-word;
}
.formula-item .expr sup,
.formula-item .expr sub {
  font-size: 0.7em;
  line-height: 0;
}
.formula-item .note {
  font-size: 11px;
  color: var(--muted);
  margin-top: 2px;
}

/* 底部导航 */
.tabbar {
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 20;
  background: rgba(255, 255, 255, .96);
  backdrop-filter: blur(10px);
  border-top: 1px solid var(--line);
  display: flex;
  padding: 6px 0 calc(6px + env(safe-area-inset-bottom));
}
.tab {
  flex: 1;
  border: 0;
  background: transparent;
  color: var(--muted);
  font-size: 11px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 4px 0;
  cursor: pointer;
}
.tab .ic { font-size: 18px; line-height: 1; }
.tab.active { color: var(--pri); font-weight: 600; }

/* 设置 */
.settings-row {
  background: var(--card);
  border-radius: 12px;
  padding: 14px 16px;
  margin-bottom: 10px;
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  gap: 10px;
}
.settings-row .grow { flex: 1; }
.settings-row .t { font-size: 15px; }
.settings-row .d { font-size: 12px; color: var(--muted); }
.import-label { display: inline-block; }

.tip {
  font-size: 12.5px;
  color: var(--muted);
  line-height: 1.7;
  padding: 2px 4px;
}
.tip b { color: var(--text); }