body{margin:0;color:#1a1a1a;max-width:640px;margin-inline:auto;padding:2rem;font-family:system-ui,-apple-system,Segoe UI,sans-serif}h1{font-size:1.5rem}section{border:1px solid #ddd;border-radius:8px;margin-bottom:2rem;padding:1rem}button{cursor:pointer;background:#fff;border:1px solid #333;border-radius:6px;padding:.5rem 1rem}button:hover{background:#f0f0f0}.error{color:#b00020}