/* 刷题页样式 — 移动端优先 */
* { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #F5F7F8;
  --card: #FFFFFF;
  --text: #0D2B45;
  --muted: #5B6B7A;
  --primary: #1565C0;
  --primary-dark: #0D47A1;
  --correct: #2E7D32;
  --correct-bg: #E8F5E9;
  --wrong: #C62828;
  --wrong-bg: #FFEBEE;
  --border: #CFD8DC;
  --radius: 12px;
}
body {
  font-family: 'Segoe UI', 'Microsoft YaHei', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-tap-highlight-color: transparent;
}
#app { max-width: 640px; margin: 0 auto; padding: 0 16px 32px; }

.topbar {
  display: flex; justify-content: space-between; align-items: center;
  padding: 16px 0; position: sticky; top: 0; background: var(--bg); z-index: 10;
}
.brand { font-weight: 700; font-size: 18px; color: var(--primary-dark); }
.stats { font-size: 14px; color: var(--muted); }

.card {
  background: var(--card); border-radius: var(--radius);
  padding: 20px; box-shadow: 0 1px 4px rgba(0,0,0,.06);
  margin-bottom: 16px;
}
.q-meta { display: flex; gap: 10px; align-items: center; margin-bottom: 12px; }
#q-number { font-weight: 700; font-size: 15px; color: var(--primary); }
.topic { font-size: 13px; color: var(--muted); background: #ECEFF1; padding: 2px 10px; border-radius: 20px; }
.q-stem { font-size: 16px; margin-bottom: 18px; white-space: pre-wrap; }

.options { display: flex; flex-direction: column; gap: 10px; margin-bottom: 16px; }
.option {
  display: flex; gap: 12px; align-items: flex-start;
  padding: 14px 16px; border: 2px solid var(--border); border-radius: 10px;
  cursor: pointer; transition: all .15s; font-size: 15px; background: #fff;
}
.option:hover { border-color: var(--primary); }
.option:active { transform: scale(.98); }
.option .letter { font-weight: 700; color: var(--primary); min-width: 20px; }
.option.correct { border-color: var(--correct); background: var(--correct-bg); }
.option.wrong { border-color: var(--wrong); background: var(--wrong-bg); }
.option.disabled { pointer-events: none; opacity: .85; }

.actions { display: flex; gap: 10px; }
.btn-ghost {
  flex: 1; padding: 12px; border: 1px solid var(--border); background: #fff;
  border-radius: 10px; font-size: 14px; color: var(--muted); cursor: pointer;
}
.btn-ghost:hover { border-color: var(--primary); color: var(--primary); }
.btn-primary {
  padding: 14px 24px; border: none; background: var(--primary); color: #fff;
  border-radius: 10px; font-size: 15px; font-weight: 600; cursor: pointer;
}
.btn-primary:hover { background: var(--primary-dark); }

.feedback {
  margin-top: 16px; padding: 14px 16px; border-radius: 10px;
  background: #F5F7F8; border-left: 4px solid var(--primary); font-size: 14px;
}
.feedback .fb-title { font-weight: 700; margin-bottom: 6px; }
.feedback .fb-hint { color: var(--muted); margin-bottom: 8px; font-style: italic; }
.feedback .fb-explain { white-space: pre-wrap; }
.feedback .btn-next {
  margin-top: 12px; width: 100%; padding: 12px; border: none;
  background: var(--primary); color: #fff; border-radius: 8px;
  font-size: 15px; font-weight: 600; cursor: pointer;
}

.empty { text-align: center; padding: 60px 20px; }
.empty-title { font-size: 24px; font-weight: 700; margin-bottom: 8px; }
.empty-sub { color: var(--muted); margin-bottom: 24px; }

.loading { text-align: center; padding: 80px 20px; color: var(--muted); }
.hidden { display: none !important; }