* { box-sizing: border-box; }
:root {
  --bg: #f4f6fb;
  --card: #ffffff;
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --danger: #dc2626;
  --text: #1f2937;
  --muted: #6b7280;
  --border: #e5e7eb;
  --ok: #16a34a;
  --warn: #d97706;
  --hl: #eef2ff;
}
html, body {
  margin: 0; padding: 0;
  font-family: -apple-system, "PingFang SC", "Microsoft YaHei", "Segoe UI", sans-serif;
  background: var(--bg); color: var(--text);
  min-height: 100vh;
}

.screen { display: none; }
.screen.active { display: block; }

/* ---- 登录 / 结果 卡片 ---- */
#screen-login, #screen-result {
  min-height: 100vh;
  padding: 32px 16px;
}
.card {
  max-width: 720px;
  margin: 0 auto;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 28px 32px;
  box-shadow: 0 4px 18px rgba(0,0,0,.04);
}
.card h1 {
  margin: 0 0 16px;
  font-size: 22px;
  letter-spacing: .5px;
}
.meta {
  display: flex; flex-wrap: wrap; gap: 10px;
  color: var(--muted); font-size: 14px;
  margin-bottom: 18px;
}
.badge {
  display: inline-block;
  padding: 2px 10px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 600;
}
.badge.open { background: #dcfce7; color: #166534; }
.notice {
  background: #f8fafc;
  border: 1px solid var(--border);
  border-left: 4px solid var(--primary);
  padding: 12px 16px;
  border-radius: 8px;
  margin-bottom: 20px;
  font-size: 14px; line-height: 1.7;
}
.notice ul { margin: 8px 0 0 18px; padding: 0; }
.notice li { margin-bottom: 4px; }

form { display: grid; gap: 12px; }
label {
  display: grid; grid-template-columns: 70px 1fr; align-items: center;
  gap: 12px; font-size: 14px;
}
input[type="text"], input:not([type]), input[type="password"] {
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 8px; font-size: 15px; outline: none;
  transition: border .15s;
}
input:focus { border-color: var(--primary); }

button {
  cursor: pointer;
  border: 1px solid var(--border);
  background: #fff;
  padding: 10px 18px;
  border-radius: 8px;
  font-size: 14px;
  transition: all .15s;
}
button:hover { background: #f3f4f6; }
button.primary {
  background: var(--primary); color: #fff; border-color: var(--primary);
}
button.primary:hover { background: var(--primary-dark); }
button.danger {
  color: var(--danger); border-color: #fecaca;
}
button.small { padding: 6px 14px; font-size: 13px; }

.teacher { margin-top: 22px; padding-top: 16px; border-top: 1px dashed var(--border); }
.teacher summary { cursor: pointer; color: var(--muted); font-size: 14px; user-select: none; }
.teacher .hint { color: var(--muted); font-size: 12px; line-height: 1.6; }
.teacher button { margin-right: 8px; margin-top: 8px; }

/* ---- 考试页 ---- */
.exam-bar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; justify-content: space-between;
  gap: 16px;
  background: #fff;
  padding: 12px 20px;
  border-bottom: 1px solid var(--border);
  box-shadow: 0 2px 8px rgba(0,0,0,.04);
}
.who { display: flex; gap: 14px; font-size: 14px; }
.who span { color: var(--muted); }
.timer {
  font-family: "JetBrains Mono", Consolas, monospace;
  font-size: 22px; font-weight: 700;
  color: var(--primary);
  background: var(--hl);
  padding: 4px 14px; border-radius: 8px;
  min-width: 100px; text-align: center;
}
.timer.warn { color: var(--warn); background: #fef3c7; }
.timer.danger { color: var(--danger); background: #fee2e2; animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: .55; } }

.progress {
  height: 4px; background: var(--border);
}
#progress-bar {
  height: 100%; width: 0%;
  background: var(--primary);
  transition: width .3s;
}

.paper {
  max-width: 880px;
  margin: 0 auto;
  padding: 24px 18px 120px;
}

.q {
  background: #fff; border: 1px solid var(--border);
  border-radius: 10px; padding: 16px 18px;
  margin-bottom: 14px;
}
.q-head {
  display: flex; align-items: center; gap: 8px;
  margin-bottom: 10px;
  font-size: 13px; color: var(--muted);
}
.q-no { font-weight: 700; color: var(--text); }
.q-tag {
  display: inline-block; padding: 1px 8px;
  border-radius: 999px; font-size: 12px;
  background: var(--hl); color: var(--primary);
}
.q-score { color: var(--warn); font-weight: 600; }
.q-stem {
  font-size: 15.5px; line-height: 1.7; margin-bottom: 12px;
  white-space: pre-wrap;
}
.opts { display: grid; gap: 8px; }
.opt {
  display: flex; align-items: flex-start; gap: 10px;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer; user-select: none;
  transition: all .12s;
  font-size: 14.5px;
}
.opt:hover { border-color: var(--primary); background: #fafbff; }
.opt.checked {
  border-color: var(--primary); background: var(--hl);
}
.opt input { margin-top: 4px; accent-color: var(--primary); }
.opt-label { font-weight: 600; min-width: 18px; }

.exam-foot {
  position: fixed; left: 0; right: 0; bottom: 0;
  background: #fff; border-top: 1px solid var(--border);
  padding: 10px 20px;
  display: flex; align-items: center; justify-content: space-between;
  gap: 12px;
  box-shadow: 0 -2px 8px rgba(0,0,0,.04);
}
#answered-count { color: var(--muted); font-size: 14px; }

/* ---- 结果页 ---- */
.score-box {
  display: grid; grid-template-columns: repeat(4, 1fr);
  gap: 12px; margin: 16px 0;
}
.score-cell {
  background: var(--hl); border-radius: 10px;
  padding: 14px; text-align: center;
}
.score-cell .v {
  font-size: 26px; font-weight: 700; color: var(--primary);
}
.score-cell .l { font-size: 12px; color: var(--muted); margin-top: 2px; }
.score-cell.total .v { color: var(--ok); font-size: 32px; }
.summary { font-size: 14px; color: var(--muted); line-height: 1.7; margin: 8px 0; }

#review { font-size: 14px; }
.review-q {
  border-bottom: 1px dashed var(--border);
  padding: 14px 0;
}
.review-q:last-child { border-bottom: none; }
.review-q .rv-head {
  display: flex; align-items: center; gap: 10px;
  font-size: 13px; color: var(--muted);
  margin-bottom: 6px;
}
.review-q .rv-tag {
  display: inline-block; padding: 1px 8px;
  border-radius: 999px; font-size: 12px;
  background: var(--hl); color: var(--primary);
}
.review-q .rv-score { font-weight: 600; margin-left: auto; }
.review-q .rv-score.ok { color: var(--ok); }
.review-q .rv-score.bad { color: var(--danger); }
.review-q .rv-stem { font-size: 14.5px; line-height: 1.7; margin-bottom: 8px; white-space: pre-wrap; }
.review-q .review-opts { margin: 6px 0 8px; display: grid; gap: 4px; }
.review-q .review-opt {
  padding: 5px 10px; border-radius: 6px; font-size: 13.5px;
  background: #fafafa; border: 1px solid transparent;
}
.review-q .review-opt .opt-letter { font-weight: 700; margin-right: 6px; color: var(--muted); }
.review-q .review-opt.is-correct {
  background: #ecfdf5; border-color: #a7f3d0; color: #065f46;
}
.review-q .review-opt.is-correct .opt-letter { color: var(--ok); }
.review-q .review-opt.is-wrong {
  background: #fef2f2; border-color: #fecaca; color: #991b1b;
}
.review-q .review-opt.is-your.is-correct::after { content: '  ← 你选的（正确）'; font-size: 12px; color: var(--ok); }
.review-q .review-opt.is-your.is-wrong::after   { content: '  ← 你选的（错误）'; font-size: 12px; color: var(--danger); }
.review-q .rv-row { font-size: 13.5px; margin: 2px 0; }
.review-q .ans { color: var(--ok); font-weight: 700; }
.review-q .your.wrong   { color: var(--danger); font-weight: 700; }
.review-q .your.correct { color: var(--ok); font-weight: 700; }
.review-q .rv-explain {
  margin-top: 8px; padding: 8px 12px;
  background: #f8fafc; border-left: 3px solid var(--primary);
  border-radius: 4px;
  font-size: 13.5px; line-height: 1.7; color: #334155;
}
.review-q .rv-explain strong { color: var(--primary); }

.actions { margin-top: 20px; display: flex; gap: 10px; }

@media (max-width: 600px) {
  label { grid-template-columns: 1fr; }
  .score-box { grid-template-columns: repeat(2, 1fr); }
  .card { padding: 20px 16px; }
}