:root {
  --background: hsl(220 20% 97%);
  --foreground: hsl(220 30% 12%);
  --card: hsl(0 0% 100%);
  --muted: hsl(220 15% 93%);
  --muted-foreground: hsl(220 10% 46%);
  --border: hsl(220 15% 88%);
  --primary: hsl(250 70% 55%);
  --primary-soft: hsl(250 70% 55% / 0.1);
  --primary-foreground: #fff;
  --success: hsl(145 65% 36%);
  --success-soft: hsl(145 65% 42% / 0.12);
  --danger: hsl(0 72% 50%);
  --danger-soft: hsl(0 75% 55% / 0.1);
  --warn: hsl(35 90% 42%);
  --code-bg: hsl(225 25% 14%);
  --code-fg: hsl(220 30% 92%);
  --shadow: 0 1px 2px hsl(220 30% 20% / 0.06), 0 4px 16px hsl(220 30% 20% / 0.05);
  --radius: 0.75rem;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --background: hsl(224 30% 8%);
    --foreground: hsl(210 40% 96%);
    --card: hsl(224 28% 12%);
    --muted: hsl(224 22% 18%);
    --muted-foreground: hsl(215 18% 66%);
    --border: hsl(224 20% 22%);
    --primary: hsl(250 85% 70%);
    --primary-soft: hsl(250 85% 70% / 0.14);
    --primary-foreground: hsl(224 30% 8%);
    --success: hsl(145 60% 55%);
    --success-soft: hsl(145 60% 50% / 0.14);
    --danger: hsl(0 80% 66%);
    --danger-soft: hsl(0 80% 60% / 0.14);
    --warn: hsl(38 90% 60%);
    --code-bg: hsl(225 30% 6%);
    --shadow: none;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --background: hsl(224 30% 8%);
  --foreground: hsl(210 40% 96%);
  --card: hsl(224 28% 12%);
  --muted: hsl(224 22% 18%);
  --muted-foreground: hsl(215 18% 66%);
  --border: hsl(224 20% 22%);
  --primary: hsl(250 85% 70%);
  --primary-soft: hsl(250 85% 70% / 0.14);
  --primary-foreground: hsl(224 30% 8%);
  --success: hsl(145 60% 55%);
  --success-soft: hsl(145 60% 50% / 0.14);
  --danger: hsl(0 80% 66%);
  --danger-soft: hsl(0 80% 60% / 0.14);
  --warn: hsl(38 90% 60%);
  --code-bg: hsl(225 30% 6%);
  --shadow: none;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--background);
  color: var(--foreground);
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, Ubuntu, sans-serif;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}
a { color: inherit; text-decoration: none; }
button { font: inherit; color: inherit; }
code, pre { font-family: ui-monospace, "JetBrains Mono", "Fira Code", Menlo, Consolas, monospace; }
:not(pre) > code { background: var(--muted); padding: 0.1em 0.35em; border-radius: 4px; font-size: 0.92em; }
.muted { color: var(--muted-foreground); }
.small { font-size: 0.85rem; }
.center { text-align: center; }

/* header */
.topbar {
  position: sticky; top: 0; z-index: 10;
  background: color-mix(in srgb, var(--background) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner { max-width: 1100px; margin: 0 auto; padding: 0.85rem 16px; display: flex; align-items: center; justify-content: space-between; }
.brand { display: flex; align-items: center; gap: 0.5rem; font-weight: 700; font-size: 1.25rem; color: var(--primary); letter-spacing: -0.01em; }
.icon-btn { background: none; border: 1px solid var(--border); border-radius: 999px; width: 38px; height: 38px; display: grid; place-items: center; cursor: pointer; color: var(--muted-foreground); }
.icon-btn:hover { color: var(--foreground); }
.icon-btn .sun { display: none; }
:root[data-theme="dark"] .icon-btn .sun { display: block; }
:root[data-theme="dark"] .icon-btn .moon { display: none; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .icon-btn .sun { display: block; }
  :root:not([data-theme="light"]) .icon-btn .moon { display: none; }
}

.container { max-width: 1100px; margin: 0 auto; padding: 1.5rem 16px 4rem; }

/* home */
.hero { text-align: center; margin: 1.5rem 0 1.5rem; }
.hero h1 { font-size: clamp(1.8rem, 4vw, 2.4rem); margin: 0 0 0.25rem; letter-spacing: -0.02em; }
.hero p { margin: 0; }
.tabs { display: flex; gap: 0.5rem; justify-content: center; flex-wrap: wrap; margin-bottom: 0.75rem; }
.tab {
  display: inline-flex; align-items: center; gap: 0.5rem; cursor: pointer;
  background: var(--card); border: 1px solid var(--border); border-radius: 999px; padding: 0.45rem 0.9rem 0.45rem 0.5rem; font-weight: 600;
}
.tab.active { border-color: var(--primary); box-shadow: 0 0 0 2px var(--primary-soft); }
.tab-count { font-size: 0.75rem; color: var(--muted-foreground); background: var(--muted); border-radius: 999px; padding: 0 0.5rem; }
.subject-blurb { text-align: center; margin: 0 0 1.5rem; }
.badge { display: inline-grid; place-items: center; min-width: 30px; height: 30px; padding: 0 6px; border-radius: 8px; font-size: 0.75rem; font-weight: 800; font-family: ui-monospace, Menlo, monospace; }
.badge-python { background: hsl(210 60% 45% / 0.15); color: hsl(210 70% 45%); }
.badge-c { background: hsl(200 15% 50% / 0.18); color: hsl(205 25% 45%); }
.badge-javascript { background: hsl(50 95% 50% / 0.25); color: hsl(45 90% 32%); }
:root[data-theme="dark"] .badge-python { color: hsl(210 80% 70%); }
:root[data-theme="dark"] .badge-c { color: hsl(205 30% 72%); }
:root[data-theme="dark"] .badge-javascript { color: hsl(50 95% 60%); }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .badge-python { color: hsl(210 80% 70%); }
  :root:not([data-theme="light"]) .badge-c { color: hsl(205 30% 72%); }
  :root:not([data-theme="light"]) .badge-javascript { color: hsl(50 95% 60%); }
}
.group-title { font-size: 1.05rem; margin: 2rem 0 0.75rem; color: var(--muted-foreground); text-transform: uppercase; letter-spacing: 0.06em; }
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 1rem; }
@media (max-width: 400px) { .grid { grid-template-columns: 1fr; } }

.card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow); }
.quiz-card { display: flex; flex-direction: column; padding: 1.15rem 1.25rem; transition: transform 0.15s, border-color 0.15s; }
.quiz-card:hover { transform: translateY(-2px); border-color: var(--primary); }
.quiz-card h3 { margin: 0; font-size: 1.05rem; line-height: 1.35; }
.quiz-card p { margin: 0.4rem 0 0.9rem; font-size: 0.92rem; flex: 1; }
.quiz-card-top { display: flex; justify-content: space-between; gap: 0.5rem; align-items: flex-start; }
.mix-card { border-style: dashed; border-color: var(--primary); background: linear-gradient(135deg, var(--primary-soft), transparent 70%), var(--card); }
.meta { display: flex; gap: 1rem; flex-wrap: wrap; font-size: 0.85rem; color: var(--muted-foreground); align-items: center; }
.meta span { display: inline-flex; align-items: center; gap: 0.35rem; }
.meta.center { justify-content: center; }
.pill { font-size: 0.72rem; font-weight: 700; padding: 0.15rem 0.55rem; border-radius: 999px; white-space: nowrap; }
.pill.good { background: var(--success-soft); color: var(--success); }
.pill.mid { background: hsl(38 90% 50% / 0.15); color: var(--warn); }
.pill.low { background: var(--danger-soft); color: var(--danger); }
.pill.new { background: var(--primary-soft); color: var(--primary); }

/* mode select */
.back-link { display: inline-flex; align-items: center; gap: 0.3rem; color: var(--muted-foreground); font-size: 0.9rem; margin-bottom: 1rem; }
.back-link:hover { color: var(--foreground); }
.mode-card { max-width: 720px; margin: 0 auto; padding: 2rem 1.5rem; text-align: center; }
.mode-card h1 { font-size: 1.6rem; margin: 0.75rem 0 0.35rem; letter-spacing: -0.01em; }
.mode-q { font-size: 1.1rem; margin: 2rem 0 1rem; }
.mode-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; }
@media (max-width: 560px) { .mode-grid { grid-template-columns: 1fr; } }
.mode-btn { display: flex; flex-direction: column; gap: 0.35rem; text-align: left; padding: 1.15rem; border-radius: var(--radius); border: 2px solid var(--border); background: var(--background); cursor: pointer; transition: border-color 0.15s, background 0.15s; }
.mode-btn strong { font-size: 1.05rem; }
.mode-btn span { font-size: 0.9rem; }
.mode-btn:hover { border-color: var(--primary); background: var(--primary-soft); }
.toggles { display: flex; gap: 1.25rem; justify-content: center; flex-wrap: wrap; margin-top: 1.5rem; font-size: 0.92rem; }
.toggle { display: inline-flex; align-items: center; gap: 0.45rem; cursor: pointer; }
.toggle input { accent-color: var(--primary); width: 16px; height: 16px; }

/* quiz */
.quiz-head { display: flex; align-items: center; justify-content: space-between; gap: 1rem; max-width: 780px; margin: 0 auto 0.5rem; }
.quiz-head .back-link { margin: 0; }
.quiz-title { font-weight: 600; font-size: 0.95rem; text-align: center; flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.timer { display: inline-flex; align-items: center; gap: 0.3rem; color: var(--muted-foreground); font-variant-numeric: tabular-nums; font-size: 0.9rem; }
.progress-row { display: flex; justify-content: space-between; font-size: 0.875rem; max-width: 780px; margin: 0.75rem auto 0.4rem; }
.progress { height: 8px; background: var(--muted); border-radius: 999px; overflow: hidden; max-width: 780px; margin: 0 auto 1.25rem; }
.progress > div { height: 100%; background: var(--primary); border-radius: 999px; transition: width 0.3s; }
.question-card { max-width: 780px; margin: 0 auto; padding: 1.5rem; }
.q-top { display: flex; justify-content: flex-end; }
.q-text { font-size: 1.2rem; margin: 0.25rem 0 1rem; line-height: 1.45; font-weight: 650; }
.code { background: var(--code-bg); color: var(--code-fg); padding: 1rem 1.1rem; border-radius: 10px; overflow-x: auto; font-size: 0.9rem; line-height: 1.55; margin: 0 0 1.25rem; }
.options { display: grid; gap: 0.65rem; }
.option {
  display: flex; align-items: center; gap: 0.8rem; text-align: left; width: 100%;
  padding: 0.8rem 1rem; border-radius: 10px; border: 2px solid var(--border); background: var(--card); cursor: pointer;
  transition: border-color 0.12s, background 0.12s;
}
.option:hover:not(:disabled) { border-color: var(--primary); }
.option .letter { flex: none; width: 28px; height: 28px; border-radius: 7px; display: grid; place-items: center; font-weight: 700; font-size: 0.85rem; background: var(--muted); }
.option .opt-text { white-space: pre-wrap; overflow-wrap: anywhere; }
.option.selected { border-color: var(--primary); background: var(--primary-soft); }
.option.selected .letter { background: var(--primary); color: var(--primary-foreground); }
.option.correct { border-color: var(--success); background: var(--success-soft); }
.option.correct .letter { background: var(--success); color: #fff; }
.option.wrong { border-color: var(--danger); background: var(--danger-soft); }
.option.wrong .letter { background: var(--danger); color: #fff; }
.option.dim { opacity: 0.6; }
.option:disabled { cursor: default; }
.feedback { margin-top: 1.25rem; padding: 1rem 1.1rem; border-radius: 10px; border-left: 4px solid; }
.feedback p { margin: 0.5rem 0 0; }
.feedback.ok { background: var(--success-soft); border-color: var(--success); }
.feedback.bad { background: var(--danger-soft); border-color: var(--danger); }
.feedback-title { display: flex; align-items: center; gap: 0.4rem; font-weight: 700; }
.feedback.ok .feedback-title { color: var(--success); }
.feedback.bad .feedback-title { color: var(--danger); }
.unanswered-warning { color: var(--warn); font-weight: 600; font-size: 0.9rem; margin: 1rem 0 0; }
.nav-row { display: flex; justify-content: space-between; gap: 0.75rem; margin-top: 1.5rem; }
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 0.4rem;
  padding: 0.6rem 1.15rem; border-radius: 9px; border: 1px solid var(--border); background: var(--card);
  cursor: pointer; font-weight: 600; font-size: 0.95rem;
}
.btn:hover:not(:disabled) { border-color: var(--primary); }
.btn.primary { background: var(--primary); border-color: var(--primary); color: var(--primary-foreground); }
.btn.primary:hover:not(:disabled) { filter: brightness(1.08); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.dots { display: flex; flex-wrap: wrap; gap: 0.4rem; justify-content: center; max-width: 780px; margin: 1.25rem auto 0; }
.dot { width: 34px; height: 34px; border-radius: 8px; border: 1px solid var(--border); background: var(--card); cursor: pointer; font-size: 0.8rem; font-weight: 600; }
.dot.answered { background: var(--primary-soft); border-color: var(--primary); color: var(--primary); }
.dot.current { outline: 2px solid var(--primary); outline-offset: 1px; }
.hint { text-align: center; margin-top: 1rem; }
@media (max-width: 560px) { .hint { display: none; } .question-card { padding: 1.1rem; } .q-text { font-size: 1.08rem; } }

/* results */
.result-card { max-width: 780px; margin: 0 auto; padding: 2rem 1.5rem; text-align: center; }
.result-card h1 { margin: 1rem 0 0.25rem; font-size: 1.5rem; }
.ring {
  --c: var(--primary);
  width: 128px; height: 128px; border-radius: 50%; margin: 0 auto; display: grid; place-items: center;
  background: conic-gradient(var(--c) calc(var(--pct) * 1%), var(--muted) 0);
}
.ring span { width: 100px; height: 100px; border-radius: 50%; background: var(--card); display: grid; place-items: center; font-size: 1.75rem; font-weight: 800; }
.result-actions { display: flex; gap: 0.6rem; justify-content: center; flex-wrap: wrap; margin-top: 1.25rem; }
.review-bar { display: flex; align-items: center; justify-content: space-between; gap: 1rem; flex-wrap: wrap; max-width: 780px; margin: 2rem auto 1rem; }
.review-bar h2 { margin: 0; font-size: 1.25rem; }
.seg { display: inline-flex; border: 1px solid var(--border); border-radius: 9px; overflow: hidden; background: var(--card); }
.seg button { border: 0; background: none; padding: 0.45rem 0.9rem; cursor: pointer; font-size: 0.88rem; font-weight: 600; color: var(--muted-foreground); }
.seg button.active { background: var(--primary); color: var(--primary-foreground); }
.review-item { max-width: 780px; margin: 0 auto 1rem; padding: 1.15rem 1.25rem; border-left: 4px solid; }
.review-item.ok { border-left-color: var(--success); }
.review-item.bad { border-left-color: var(--danger); }
.review-head { display: flex; gap: 0.6rem; align-items: flex-start; }
.review-head h3 { margin: 0 0 0.75rem; font-size: 1.02rem; line-height: 1.45; }
.review-item.ok .status { color: var(--success); }
.review-item.bad .status { color: var(--danger); }
.status { flex: none; margin-top: 2px; }
.review-options { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; gap: 0.35rem; }
.review-options li { display: flex; align-items: center; gap: 0.6rem; padding: 0.4rem 0.6rem; border-radius: 7px; font-size: 0.93rem; }
.review-options li span:nth-child(2) { white-space: pre-wrap; overflow-wrap: anywhere; }
.review-options .letter { flex: none; width: 22px; height: 22px; border-radius: 5px; display: grid; place-items: center; font-weight: 700; font-size: 0.75rem; background: var(--muted); }
.review-options li.correct { background: var(--success-soft); }
.review-options li.correct .letter { background: var(--success); color: #fff; }
.review-options li.wrong { background: var(--danger-soft); }
.review-options li.wrong .letter { background: var(--danger); color: #fff; }
.review-options em { margin-left: auto; font-size: 0.75rem; font-style: normal; font-weight: 700; color: var(--muted-foreground); white-space: nowrap; padding-left: 0.5rem; }
.why, .explain { margin: 0.4rem 0 0; font-size: 0.93rem; }
.why strong { color: var(--danger); }
.explain strong { color: var(--success); }
.notfound { max-width: 480px; margin: 3rem auto; padding: 2rem; }
.notfound h1 { font-size: 3rem; margin: 0; }

/* speedrun */
.top-actions { display: flex; align-items: center; gap: 0.5rem; }
.top-link { display: inline-flex; align-items: center; gap: 0.35rem; height: 38px; padding: 0 0.85rem; border: 1px solid var(--border); border-radius: 999px; font-weight: 600; font-size: 0.9rem; color: var(--foreground); }
.top-link:hover { border-color: var(--warn); color: var(--warn); }
.badge-all { background: var(--primary-soft); color: var(--primary); }
.speed-entry { border-style: dashed; border-color: var(--warn); background: linear-gradient(135deg, hsl(38 90% 50% / 0.12), transparent 70%), var(--card); }
.speed-entry h3, .speed-mode h3 { display: inline-flex; align-items: center; gap: 0.4rem; }
.speed-entry h3 svg, .speed-mode h3 svg { color: var(--warn); flex: none; }
.speed-countdown { max-width: 420px; margin: 3rem auto; padding: 2.5rem 1rem; }
.speed-countdown .count { font-size: 5rem; font-weight: 800; line-height: 1.1; color: var(--primary); animation: count-pop 0.6s ease-out; }
.run-clock { font-variant-numeric: tabular-nums; font-weight: 700; }
.progress-row .speed-flash { font-weight: 800; opacity: 0; }
.speed-flash.ok { color: var(--success); }
.speed-flash.bad { color: var(--danger); }
.speed-flash.show { animation: flash-up 0.9s ease-out; }
#run-bar { transition: width 0.1s linear; }
.progress.low > div { background: var(--danger); }
.speed-score { font-size: 3rem; font-weight: 800; line-height: 1.1; margin-top: 0.5rem; color: var(--primary); font-variant-numeric: tabular-nums; }
@keyframes count-pop { from { transform: scale(1.6); opacity: 0; } to { transform: none; opacity: 1; } }
@keyframes flash-up { 0% { opacity: 0; transform: translateY(6px); } 15% { opacity: 1; transform: none; } 70% { opacity: 1; } 100% { opacity: 0; transform: translateY(-8px); } }
@media (prefers-reduced-motion: reduce) {
  .speed-countdown .count, .speed-flash.show { animation: none; }
  .speed-flash.show { opacity: 1; }
}
@media (max-width: 560px) { .top-link span { display: none; } .top-link { width: 38px; padding: 0; justify-content: center; } }