*{box-sizing:border-box}body{margin:0;min-height:100vh;display:flex;align-items:center;justify-content:center;font-family:system-ui,-apple-system,sans-serif;background:#f5f5f5}.challenge{text-align:center;padding:2rem}.spinner{width:40px;height:40px;margin:0 auto 1rem;border:3px solid #e0e0e0;border-top-color:#2563eb;border-radius:50%;animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.message{margin:0;color:#444;font-size:1rem}.challenge.error .message{color:#b91c1c}