span.ie-bug-fix {
  display: block;
  float: left;
  height: 100%;
  width: 100%;
 	z-index: 0;
 	position: absolute;
 	top: 0;
 	left: 0;	
}

#bandeau-haut span.ie-bug-fix {
  background: #fff;
  filter: alpha(opacity=30);   
	-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=30)";
}

ul#menu-principal {
  float: left;
 	position: absolute;
 	top: 0;
 	left: 0;	
	z-index: 20;
}
#bandeau-bas span.ie-bug-fix {
  background: #000;
  filter: alpha(opacity=60);   
	-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=60)";
}