body{font-family:Arial,sans-serif;text-align:center}h1{margin-top:20px}.calculator{width:300px;margin:0 auto;padding:20px;border:1px solid #ccc;border-radius:5px;background-color:#f5f5f5}label{font-weight:700}input{width:100%;padding:5px;margin-bottom:10px}button{width:100%;padding:10px;background-color:#007BFF;color:#fff;border:none;cursor:pointer}.result{width:300px;margin:20px auto;text-align:center}