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}#display{width:100%;padding:10px;margin-bottom:10px;font-size:24px;text-align:right}.buttons{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}button{padding:15px;font-size:18px;border:none;background-color:#007BFF;color:#fff;cursor:pointer}button:hover{background-color:#0056b3}