:root{color-scheme:light dark;--bg:#fff;--fg:#111827;--muted-fg:#6b7280;--border:#e5e7eb;--surface:#fff;--surface-2:#f9fafb;--surface-hover:#f3f4f6;--accent-green:#16a34a;--accent-red:#dc2626;--tint-green:rgba(22,163,74,.12);--tint-red:rgba(220,38,38,.12);--focus:#6366f1}@media (prefers-color-scheme:dark){:root{--bg:#0b1220;--fg:#e5e7eb;--muted-fg:#9ca3af;--border:#2a2f3a;--surface:#111827;--surface-2:#0f172a;--surface-hover:#1f2937;--tint-green:rgba(22,163,74,.18);--tint-red:rgba(220,38,38,.18);--focus:#818cf8}}*{box-sizing:border-box}body{margin:0;font-family:ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Helvetica,Arial,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol;line-height:1.6;padding:24px;background:var(--bg);color:var(--fg)}.container{max-width:720px;margin:0 auto}.card{border:1px solid var(--border);border-radius:12px;padding:16px;margin-bottom:16px;background:var(--surface)}.button{padding:10px 14px;border-radius:8px;border:1px solid var(--border);background:var(--surface-2);color:var(--fg);cursor:pointer;transition:background-color .15s ease,border-color .15s ease,box-shadow .15s ease}.button:hover:not(:disabled){background:var(--surface-hover)}.button:disabled{opacity:.6;cursor:not-allowed}.button:focus-visible,.choice:focus-visible{outline:2px solid var(--focus);outline-offset:2px}.choice{display:block;width:100%;text-align:left;padding:12px 14px;border:1px solid var(--border);border-radius:10px;margin:8px 0;background:var(--surface);color:var(--fg);transition:background-color .15s ease,border-color .15s ease,box-shadow .15s ease}.choice:hover:not(:disabled){background:var(--surface-hover)}.choice:disabled{opacity:.9;cursor:not-allowed}.choice.correct{border-color:var(--accent-green);background:var(--tint-green)}.choice.incorrect{border-color:var(--accent-red);background:var(--tint-red)}.feedback{font-size:14px;color:var(--muted-fg);margin-top:4px}.explanation{margin-top:16px;padding:12px;background:var(--surface-2);border:1px solid var(--border);border-radius:10px;color:var(--fg)}