body {
    background-image: url("/Content/images/login-background.jpg");
}

.login-box {
    width: 500px;
    height: 400px;
    background-color: white;
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    padding:20px;
    margin: auto;
}