html, body {
   margin:0;
   padding:0;  
   height:100%; 
}

#Layer1{
position: absolute;
top: 50%;
left: 50%;
height: 480px;
width: 480px;
margin: -240px 0 0 -240px;
border: 1px solid #000;
} 


div.transOFF {width: 100%; }

div.transON  {width: 100%;opacity:.50;filter: alpha(opacity=50); -moz-opacity: 0.50; 
}