/* ===== Design tokens ===== */
:root {
  --bg: #f3f6f8;
  --surface: #ffffff;
  --surface-alt: #e9eef3;
  --text: #16212e;
  --text-dim: #5c6b7e;
  --border: #d7dfe6;
  --accent: #0e7c86;
  --accent-ink: #075158;
  --accent-soft: #e2f2f2;
  --good: #1a7f4e;
  --good-soft: #e5f6ec;
  --bad: #c0362c;
  --bad-soft: #fdecea;
  --warn: #a8730c;
  --warn-soft: #fbf1dc;
  --radius-lg: 18px;
  --radius-md: 12px;
  --radius-sm: 8px;
  --shadow: 0 1px 2px rgba(22, 33, 46, 0.06), 0 8px 24px -12px rgba(22, 33, 46, 0.12);
  padding-top: env(safe-area-inset-top, 0px);
  padding-bottom: env(safe-area-inset-bottom, 0px);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0a1220;
    --surface: #121c2d;
    --surface-alt: #1a2740;
    --text: #e6edf5;
    --text-dim: #93a3ba;
    --border: #263652;
    --accent: #3ecfcf;
    --accent-ink: #bdf3f3;
    --accent-soft: #113135;
    --good: #45d488;
    --good-soft: #103524;
    --bad: #ff6f66;
    --bad-soft: #3a1917;
    --warn: #e8b64a;
    --warn-soft: #362b10;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px -12px rgba(0, 0, 0, 0.5);
  }
}
:root[data-theme="dark"] {
  --bg: #0a1220;
  --surface: #121c2d;
  --surface-alt: #1a2740;
  --text: #e6edf5;
  --text-dim: #93a3ba;
  --border: #263652;
  --accent: #3ecfcf;
  --accent-ink: #bdf3f3;
  --accent-soft: #113135;
  --good: #45d488;
  --good-soft: #103524;
  --bad: #ff6f66;
  --bad-soft: #3a1917;
  --warn: #e8b64a;
  --warn-soft: #362b10;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 8px 24px -12px rgba(0, 0, 0, 0.5);
}

/* ===== Base ===== */
* { box-sizing: border-box; }
html, body { height: auto; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Noto Sans TC", "PingFang TC", "Microsoft JhengHei", sans-serif;
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
.mono { font-family: "IBM Plex Mono", ui-monospace, SFMono-Regular, Menlo, monospace; font-variant-numeric: tabular-nums; }
h1, h2, h3 { text-wrap: balance; margin: 0; }
button { font-family: inherit; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
[hidden] { display: none !important; }

/* ===== Topbar ===== */
.topbar {
  position: sticky;
  top: env(safe-area-inset-top, 0px);
  z-index: 20;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  max-width: 760px;
  margin: 0 auto;
  padding: 14px 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}
.brand { display: flex; align-items: center; gap: 10px; min-width: 0; }
.brand-mark {
  flex: none;
  width: 32px; height: 32px;
  border-radius: 8px;
  background: var(--accent);
  color: var(--surface);
  display: grid; place-items: center;
  font-family: "IBM Plex Mono", monospace;
  font-weight: 600;
  font-size: 13px;
}
.brand-text {
  font-weight: 700;
  font-size: 14px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.brand-text em { display: block; font-style: normal; font-weight: 500; font-size: 11px; color: var(--text-dim); }
.exam-meta { flex: none; display: flex; align-items: center; gap: 8px; font-size: 13px; color: var(--text-dim); }
.exam-meta .dot { opacity: .5; }
#examTimer { color: var(--text); font-weight: 500; }
.progress-bar { height: 3px; background: var(--surface-alt); }
.progress-bar-fill { height: 100%; background: var(--accent); width: 0%; transition: width .25s ease; }

/* ===== Layout ===== */
#app { max-width: 760px; margin: 0 auto; padding: 28px 20px 64px; }
.view { display: flex; flex-direction: column; gap: 28px; }

/* ===== Start screen ===== */
.hero { display: flex; flex-direction: column; gap: 14px; padding-top: 8px; }
.eyebrow {
  margin: 0; font-family: "IBM Plex Mono", monospace; font-size: 12px; letter-spacing: .08em;
  text-transform: uppercase; color: var(--accent-ink); background: var(--accent-soft);
  display: inline-block; padding: 4px 10px; border-radius: 999px; width: fit-content;
}
.hero h1 { font-size: clamp(28px, 6vw, 38px); font-weight: 900; letter-spacing: -.01em; }
.lede { margin: 0; color: var(--text-dim); font-size: 15px; max-width: 62ch; }

.stat-row { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; }
.stat-tile {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-md);
  padding: 14px 10px; text-align: center; display: flex; flex-direction: column; gap: 4px;
}
.stat-num { font-size: 22px; font-weight: 600; color: var(--accent-ink); }
.stat-label { font-size: 11px; color: var(--text-dim); }

.unit-list { display: flex; flex-direction: column; gap: 8px; }
.unit-chip {
  display: flex; align-items: center; gap: 10px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 10px 14px; font-size: 14px;
}
.unit-no { color: var(--text-dim); font-size: 12px; }

.btn { border: none; cursor: pointer; border-radius: var(--radius-sm); font-weight: 700; transition: transform .08s ease, opacity .15s ease; }
.btn:active { transform: scale(.98); }
.btn-primary { background: var(--accent); color: var(--surface); }
.btn-primary:hover { opacity: .92; }
.btn-accent { background: var(--good); color: var(--surface); }
.btn-ghost { background: transparent; color: var(--text); border: 1px solid var(--border); }
.btn-lg { padding: 15px 20px; font-size: 16px; width: 100%; }
.btn:disabled { opacity: .4; cursor: not-allowed; }
.btn-link { background: none; border: none; color: var(--text-dim); text-decoration: underline; cursor: pointer; font-size: 13px; padding: 0; width: fit-content; }

.fine-print { font-size: 12.5px; color: var(--text-dim); line-height: 1.7; margin: 0; }

.history-block { display: flex; flex-direction: column; gap: 10px; border-top: 1px solid var(--border); padding-top: 20px; }
.history-block h2 { font-size: 14px; color: var(--text-dim); font-weight: 700; }
.history-list { display: flex; flex-direction: column; gap: 6px; }
.history-row {
  display: flex; align-items: center; justify-content: space-between; gap: 10px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-sm);
  padding: 9px 12px; font-size: 13px;
}
.history-row .h-date { color: var(--text-dim); }
.history-row .h-score { font-family: "IBM Plex Mono", monospace; font-weight: 600; }
.history-pill { font-size: 11px; font-weight: 700; padding: 2px 8px; border-radius: 999px; }
.history-pill.pass { background: var(--good-soft); color: var(--good); }
.history-pill.fail { background: var(--bad-soft); color: var(--bad); }

/* ===== Question map ===== */
.question-map {
  display: flex; flex-wrap: wrap; gap: 6px;
  padding: 10px; background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-md);
}
.qmap-btn {
  width: 30px; height: 30px; border-radius: 7px; border: 1px solid var(--border);
  background: var(--surface-alt); color: var(--text-dim); font-family: "IBM Plex Mono", monospace;
  font-size: 12px; cursor: pointer; display: grid; place-items: center;
}
.qmap-btn.is-answered { background: var(--accent-soft); color: var(--accent-ink); border-color: var(--accent); }
.qmap-btn.is-current { outline: 2px solid var(--accent); outline-offset: 1px; font-weight: 700; }

/* ===== Question card ===== */
.question-card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 22px; box-shadow: var(--shadow); display: flex; flex-direction: column; gap: 16px;
}
.question-head { display: flex; gap: 8px; }
.chip { font-size: 11.5px; font-weight: 700; padding: 4px 10px; border-radius: 999px; letter-spacing: .02em; }
.chip-topic { background: var(--surface-alt); color: var(--text-dim); }
.chip-type { background: var(--accent-soft); color: var(--accent-ink); }
.chip-type.is-multi { background: var(--warn-soft); color: var(--warn); }
.question-text { font-size: 18px; font-weight: 700; line-height: 1.55; }

.options { display: flex; flex-direction: column; gap: 10px; }
.option {
  display: flex; align-items: flex-start; gap: 12px;
  border: 1px solid var(--border); border-radius: var(--radius-md);
  padding: 13px 15px; cursor: pointer; background: var(--surface);
}
.option:hover { border-color: var(--accent); }
.option input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.option-letter {
  flex: none; width: 26px; height: 26px; border-radius: 7px; background: var(--surface-alt);
  color: var(--text-dim); font-family: "IBM Plex Mono", monospace; font-size: 12px; font-weight: 600;
  display: grid; place-items: center;
}
.option-text { font-size: 15px; padding-top: 2px; }
.option.is-selected { border-color: var(--accent); background: var(--accent-soft); }
.option.is-selected .option-letter { background: var(--accent); color: var(--surface); }

.exam-nav { display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.exam-nav .btn { padding: 12px 18px; font-size: 14px; }
.answered-count { font-size: 12.5px; color: var(--text-dim); }

/* ===== Result screen ===== */
.result-summary {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 28px 22px; text-align: center; box-shadow: var(--shadow);
  display: flex; flex-direction: column; align-items: center; gap: 10px;
}
.result-pill { font-size: 12px; font-weight: 800; letter-spacing: .08em; padding: 5px 14px; border-radius: 999px; }
.result-pill.pass { background: var(--good-soft); color: var(--good); }
.result-pill.fail { background: var(--bad-soft); color: var(--bad); }
.result-score { display: flex; align-items: baseline; gap: 6px; margin-top: 4px; }
#resultScoreNum { font-size: 52px; font-weight: 700; }
.result-score-suffix { color: var(--text-dim); font-size: 15px; }
.result-sub { margin: 0; color: var(--text-dim); font-size: 14px; }
.result-breakdown { display: flex; gap: 24px; margin-top: 10px; }
.breakdown-item { display: flex; flex-direction: column; align-items: center; gap: 2px; }
.breakdown-item span { font-size: 16px; font-weight: 600; }
.breakdown-item label { font-size: 11.5px; color: var(--text-dim); }
.result-actions { display: flex; gap: 10px; margin-top: 14px; width: 100%; }
.result-actions .btn { flex: 1; padding: 13px; font-size: 14px; }

.review-controls { display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.review-controls h2 { font-size: 18px; font-weight: 800; }
.filter-tabs { display: flex; gap: 6px; background: var(--surface-alt); padding: 4px; border-radius: 999px; }
.filter-tab { border: none; background: none; padding: 6px 14px; border-radius: 999px; font-size: 13px; font-weight: 600; color: var(--text-dim); cursor: pointer; }
.filter-tab.is-active { background: var(--surface); color: var(--text); box-shadow: var(--shadow); }

.review-list { display: flex; flex-direction: column; gap: 14px; }
.review-item {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 20px; display: flex; flex-direction: column; gap: 12px;
}
.review-item.is-wrong { border-color: color-mix(in srgb, var(--bad) 45%, var(--border)); }
.review-head { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.review-index { font-family: "IBM Plex Mono", monospace; font-size: 12.5px; color: var(--text-dim); }
.review-status { margin-left: auto; font-size: 12px; font-weight: 700; padding: 3px 10px; border-radius: 999px; }
.review-status.correct { background: var(--good-soft); color: var(--good); }
.review-status.wrong { background: var(--bad-soft); color: var(--bad); }
.review-question { font-size: 16px; font-weight: 700; line-height: 1.55; }
.review-options { display: flex; flex-direction: column; gap: 8px; }
.review-option {
  display: flex; align-items: flex-start; gap: 10px; border: 1px solid var(--border);
  border-radius: var(--radius-sm); padding: 10px 12px; font-size: 14px;
}
.review-option .option-letter { width: 22px; height: 22px; font-size: 11px; }
.review-option.opt-correct { border-color: var(--good); background: var(--good-soft); }
.review-option.opt-correct .option-letter { background: var(--good); color: var(--surface); }
.review-option.opt-user-wrong { border-color: var(--bad); background: var(--bad-soft); }
.review-option.opt-user-wrong .option-letter { background: var(--bad); color: var(--surface); }
.review-option-tag { margin-left: auto; font-size: 11px; font-weight: 700; flex: none; }
.review-option.opt-correct .review-option-tag { color: var(--good); }
.review-option.opt-user-wrong .review-option-tag { color: var(--bad); }
.review-explain {
  background: var(--surface-alt); border-radius: var(--radius-sm); padding: 12px 14px;
  font-size: 13.5px; color: var(--text-dim); line-height: 1.7;
}
.review-explain b { color: var(--text); }

/* ===== Confirm overlay ===== */
.confirm-overlay {
  position: fixed; inset: 0; background: rgba(10, 15, 25, .5); display: grid; place-items: center;
  padding: 20px; z-index: 50;
}
.confirm-box {
  background: var(--surface); border-radius: var(--radius-lg); padding: 22px; max-width: 340px;
  width: 100%; box-shadow: var(--shadow); display: flex; flex-direction: column; gap: 16px;
}
.confirm-box p { margin: 0; font-size: 14.5px; line-height: 1.6; }
.confirm-actions { display: flex; gap: 10px; }
.confirm-actions .btn { flex: 1; padding: 11px; font-size: 14px; }

/* ===== Responsive ===== */
@media (max-width: 480px) {
  .stat-row { grid-template-columns: repeat(2, 1fr); }
  .result-breakdown { gap: 16px; }
  #resultScoreNum { font-size: 42px; }
}