.trans50 {
    -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";
    filter: alpha(opacity=50);
    -khtml-opacity: 0.5;
    -moz-opacity: 0.5;
    opacity: 0.5;
}
.hidden {
    -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";
    filter: alpha(opacity=0);
    -khtml-opacity: 0;
    -moz-opacity: 0;
    opacity: 0;
}