.sitecontainer{
max-width:1600px;
margin:auto;
}

.loginbox{
    position:fixed;
    top:50%;
    left:50%;
    transform:translate(-50% , -50%);
    border:solid 1px #dcdcdc;
    border-radius:10px;
    box-shadow:0 0 15px #dcdcdc;
    padding:15px;
}