#page_screen
{
   background-color:#000000;
   filter:alpha(opacity=50);
   opacity: 0.5;
   -moz-opacity:0.5; 
   position:absolute;
   top:0px;
   left:0px;
   width:100%;
   height: 150%;
   display:none;
   z-index:-1; /* 4000 */
}