:root {
  --bg: #ffffff;
  --fg: #1a1a24;
  --muted: #5c5c6e;
  --card: #f6f7f9;
  --border: #d9dbe1;
  --accent: #007d9c; /* Go blue-teal */
  --accent-fg: #ffffff;
  --correct-bg: #e6f4ea;
  --correct-border: #34a853;
  --wrong-bg: #fdecea;
  --wrong-border: #d93025;
  --code-bg: #0f1117;
  --code-fg: #e6e6ef;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1117;
    --fg: #e6e6ef;
    --muted: #9a9ab0;
    --card: #1a1d26;
    --border: #33374a;
    --accent: #29b6d8;
    --accent-fg: #0f1117;
    --correct-bg: #12301c;
    --correct-border: #4ec97a;
    --wrong-bg: #391b18;
    --wrong-border: #f28b82;
    --code-bg: #05060a;
  }
}

* { box-sizing: border-box; }
body {
  margin: 0 auto;
  max-width: 46rem;
  padding: 1.25rem 1rem 3rem;
  font-family: "Hiragino Sans", "Noto Sans JP", system-ui, sans-serif;
  line-height: 1.7;
  background: var(--bg);
  color: var(--fg);
}
header h1 { margin: 0; font-size: 1.6rem; }
.tagline { margin: 0.25rem 0 1.5rem; color: var(--muted); font-size: 0.9rem; }

button {
  font: inherit;
  cursor: pointer;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--fg);
  padding: 0.6rem 1rem;
}
button.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-fg);
  font-weight: 600;
}
button:disabled { opacity: 0.55; cursor: default; }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.1rem 1.25rem;
  margin-bottom: 1rem;
}

.topic-picker { margin: 0.75rem 0 1.25rem; }
.topic-picker summary {
  cursor: pointer;
  color: var(--accent);
  font-size: 0.9rem;
  list-style: none;
}
.topic-picker summary::-webkit-details-marker { display: none; }
.topic-picker summary::before { content: "▸ "; }
.topic-picker[open] summary::before { content: "▾ "; }

.topic-list { display: flex; flex-wrap: wrap; gap: 0.5rem; margin: 0.75rem 0 0; }
.release-list { display: flex; flex-direction: column; gap: 0.5rem; margin: 0.75rem 0 0; }
.release-list button { text-align: left; }
.section-title { margin: 0 0 0.4rem; font-size: 1.05rem; }
.section-desc { margin: 0 0 0.75rem; font-size: 0.9rem; color: var(--muted); }
.topic-list button.selected {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-fg);
}

.meta { color: var(--muted); font-size: 0.85rem; margin-bottom: 0.5rem; }

pre.code {
  background: var(--code-bg);
  color: var(--code-fg);
  border-radius: 10px;
  padding: 1rem;
  overflow-x: auto;
  font-size: 0.9rem;
  line-height: 1.55;
}
code, pre { font-family: "SF Mono", Menlo, Consolas, monospace; }

.choices { display: flex; flex-direction: column; gap: 0.5rem; margin: 1rem 0; }
.choices button {
  text-align: left;
  white-space: pre-wrap;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.9rem;
}
.choices button.correct { background: var(--correct-bg); border-color: var(--correct-border); }
.choices button.wrong { background: var(--wrong-bg); border-color: var(--wrong-border); }

.feedback { border-radius: 10px; padding: 0.9rem 1rem; margin: 1rem 0; }
.feedback.correct { background: var(--correct-bg); border: 1px solid var(--correct-border); }
.feedback.wrong { background: var(--wrong-bg); border: 1px solid var(--wrong-border); }
.feedback h3 { margin: 0 0 0.4rem; font-size: 1rem; }

.spec-refs { margin: 0.75rem 0 0; padding-left: 1.2rem; font-size: 0.9rem; }
.spec-refs a { color: var(--accent); word-break: break-all; }

.controls { display: flex; gap: 0.6rem; flex-wrap: wrap; align-items: center; }
.copy-fallback {
  width: 100%;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.85rem;
  padding: 0.45rem 0.6rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--fg);
}
.progress { color: var(--muted); font-size: 0.85rem; margin-bottom: 0.75rem; }

footer { margin-top: 2.5rem; color: var(--muted); font-size: 0.8rem; border-top: 1px solid var(--border); padding-top: 1rem; }
footer a { color: var(--accent); }

.stats { font-size: 0.9rem; color: var(--muted); }
.danger { color: var(--wrong-border); }