.ecran {
display:none;
position:absolute;
z-index:20000;
background-color:#000;
-moz-opacity: 0.7;
opacity:.70;
filter: alpha(opacity=70);
top:0%;
left:0%;
width:100%;
height:100%;
}

.voeux {
position:absolute;
z-index:30000;
background-color:#000;
top:50%;
left:50%;
width:828px;
height:410px;
margin-left: -414px;
margin-top: -205px;
}