:root {
  color-scheme: light dark;
  --bg: #fafafa;
  --fg: #1a1a1a;
  --accent: #c0392b;
  --card-bg: #fff;
  --border: #e0e0e0;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16171a;
    --fg: #eee;
    --card-bg: #222327;
    --border: #333;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--fg);
}
.topnav {
  display: flex;
  gap: 1.5rem;
  align-items: center;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border);
}
.topnav .brand { font-weight: bold; font-size: 1.1rem; margin-right: auto; }
.topnav a { color: inherit; text-decoration: none; }
.topnav a:hover { color: var(--accent); }
main { max-width: 640px; margin: 0 auto; padding: 1.5rem; }
.cards { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1rem; }
.card {
  display: flex;
  flex-direction: column;
  padding: 1.25rem;
  border-radius: 10px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  text-decoration: none;
  color: inherit;
}
.card-number { font-size: 2rem; font-weight: bold; color: var(--accent); }
.card-label { color: inherit; opacity: 0.8; }
.card.muted .card-number { color: inherit; opacity: 0.6; }
.lesson-list { list-style: none; padding: 0; }
.lesson-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 1rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 0.75rem;
  background: var(--card-bg);
}
.example { font-size: 0.85rem; opacity: 0.75; margin-top: 0.25rem; }
button {
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1rem;
}
input[type="text"] {
  padding: 0.5rem;
  font-size: 1rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  margin-right: 0.5rem;
}
.prompt { font-size: 1.3rem; }
.result { padding: 0.75rem 1rem; border-radius: 8px; margin-bottom: 1rem; }
.result.correct { background: #d4edda; color: #155724; }
.result.incorrect { background: #f8d7da; color: #721c24; }