*{box-sizing:border-box}body{margin:0;font-family:Arial,sans-serif;background:#f4f4f4;color:#222}.app{max-width:640px;margin:40px auto;padding:20px;border:1px solid #ddd;border-radius:8px;background:#fff}.task-form{display:flex;gap:8px;margin-bottom:16px}.task-form input{flex:1;padding:8px}.task-form button,.task-list button{padding:8px 10px;cursor:pointer}.error{color:#c62828}.task-list{list-style:none;padding:0;margin:0}.task-list li{display:flex;justify-content:space-between;align-items:center;gap:12px;padding:10px 0;border-bottom:1px solid #eee}.task-list li.done span{text-decoration:line-through;color:#777}