html, body { background-color: #f1f1f1; font-family: Arial, Helvetica, sans-serif; } .center { position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%); border: 5px solid gray; padding: 10px; } #main { background-color: #fff; width: 400px; padding: 5px; text-align: center; }