.conteneurindex {
position:absolute;
left: 50%; 
top: 50%;
width: 850px;
height: 470px;
margin-top: -235px;
margin-left: -425px;
border: 0px solid #000000;
z-index:1;
}
.conteneur {
position:absolute;
left: 50%; 
top: 50%;
width: 822px;
height: 580px;
margin-top: -290px;
margin-left: -411px;
border: 0px solid #000000;
z-index:1;
}