透明度
width: 100%;height: 100%;
-ms-filter:'progid:DXImageTransform.Microsoft.Alpha(Opacity=50)';/* IE 8 */
filter: alpha(opacity=50); /* IE 4-7 */
position: fixed; top:0;left:0;background-color:black;-moz-opacity:0.5;opacity: 0.5; z-index: 10;
-ms-filter:'progid:DXImageTransform.Microsoft.Alpha(Opacity=50)';/* IE 8 */
filter: alpha(opacity=50); /* IE 4-7 */
position: fixed; top:0;left:0;background-color:black;-moz-opacity:0.5;opacity: 0.5; z-index: 10;