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; 
}