body {
    background: url(/images/loginbg.jpg);
    background-size: cover;
    background-attachment: fixed;
    background-position: center;
}

#loginBox {
    position: absolute;
    z-index: 10;
    width: 90%;
    max-width: 400px;
    left: 0;
    right: 0;
    margin-left: auto;
    margin-right: auto;
    top: 3vw;
}