:root {
  --bg: #f5f6f8;
  --card: #ffffff;
  --ink: #1c2230;
  --muted: #6b7280;
  --line: #e4e7ec;
  --accent: #2f6df6;
  --accent-ink: #ffffff;
  --good: #157347;
  --bad: #b02a37;
  --accel-bg: #eef4ff;
  --radius: 14px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.5;
}

.topbar {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 16px 24px;
  border-bottom: 1px solid var(--line);
  background: var(--card);
}
.brand { font-weight: 700; font-size: 1.25rem; color: var(--ink); text-decoration: none; }
.tagline { color: var(--muted); font-size: 0.9rem; }

.wrap { max-width: 640px; margin: 0 auto; padding: 24px 16px 48px; }

.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 18px;
}
.card.subtle { background: transparent; border-style: dashed; }
.card.accel { background: var(--accel-bg); border-color: #cfe0ff; }

h1 { margin: 0 0 12px; font-size: 1.6rem; }
h2 { margin: 4px 0 12px; font-size: 1.15rem; }
.stem { font-size: 1.5rem; letter-spacing: 0.2px; }
.figure { margin: 16px 0 4px; display: flex; justify-content: center; }
.figure svg { max-width: 100%; height: auto; background: #fff; border-radius: 8px; padding: 4px; }

.muted { color: var(--muted); }
.small { font-size: 0.9rem; }
.center { text-align: center; }

.stack { display: flex; flex-direction: column; gap: 10px; }
.row { display: flex; gap: 10px; flex-wrap: wrap; }
.row input { flex: 1; min-width: 180px; }

label { font-weight: 600; font-size: 0.95rem; }
input[type="text"] {
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 10px;
  font-size: 1rem;
  background: #fff;
}

button {
  font-size: 1rem;
  padding: 12px 18px;
  border-radius: 10px;
  border: 1px solid var(--line);
  background: #fff;
  cursor: pointer;
}
button.primary, .btn {
  background: var(--accent);
  color: var(--accent-ink);
  border-color: var(--accent);
  font-weight: 600;
  text-decoration: none;
  display: inline-block;
  padding: 12px 20px;
  border-radius: 10px;
}
button:hover { filter: brightness(0.97); }

.choices { display: flex; flex-direction: column; gap: 12px; margin-top: 8px; }
.choice {
  text-align: left;
  font-size: 1.15rem;
  padding: 16px 18px;
  background: #fff;
  border: 2px solid var(--line);
}
.choice:hover { border-color: var(--accent); background: #f7f9ff; }

.result-grid { display: flex; gap: 16px; flex-wrap: wrap; margin: 8px 0 4px; }
.stat {
  flex: 1; min-width: 200px;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 14px 16px;
}
.stat-label { display: block; color: var(--muted); font-size: 0.85rem; }
.stat-value { display: block; font-size: 1.3rem; font-weight: 700; margin-top: 2px; }

.gaps { list-style: none; padding: 0; margin: 8px 0 0; }
.gaps li { padding: 8px 0; border-bottom: 1px solid var(--line); }
.pill, .tag {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 600;
  padding: 2px 8px;
  border-radius: 999px;
  background: #eef1f5;
  color: var(--muted);
  margin-right: 6px;
}

.missed { border-top: 1px solid var(--line); padding: 14px 0; }
.missed:first-of-type { border-top: none; }
.line { margin: 4px 0; }
.tag.wrong { background: #fdecee; color: var(--bad); }
.tag.right { background: #e8f5ee; color: var(--good); }
.explain { margin: 8px 0 0; color: var(--ink); background: #fbfbfc; border-left: 3px solid var(--accent); padding: 8px 12px; border-radius: 6px; }

.code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 1.8rem;
  letter-spacing: 4px;
  font-weight: 700;
  background: #f2f4f8;
  padding: 10px 16px;
  border-radius: 10px;
  display: inline-block;
}

.foot { max-width: 640px; margin: 0 auto; padding: 0 16px 32px; color: var(--muted); }