div.popup{
position:absolute;
background:#F4F4F4;
left:50%;
top:50%;
width:600px;
height:150px;
margin-left:-300px;
margin-top:-200px;
z-index:1;
padding:20px;
border:1px solid #666666;
}

div#over {
position:absolute;
left:0;
top:0;
background:black;
height:100%;
width:100%;
z-index:1;
}