#overlay {
     visibility: visible;
     position: absolute;
     left: 0px;
     top: 0px;
     width:110%;
     height:200%;
     text-align:center;
     z-index: 1000;
     background-image:url(overlay.gif);
}
#overlay div {
     width:600px;
     margin: 100px auto;
     background-color: #fff;
     border:1px solid #000;
     padding:15px;
     text-align:center;
}