css之IE透明度

.bg{
   /*Filter for IE8 */    
   -ms-filter: "progid:DXImageTransform.Microsoft.gradient(GradientType=1,startColorstr=#80000000,endColorstr=#80000000)";
   /*Filter for older IEs */
   filter: progid:DXImageTransform.Microsoft.gradient(GradientType=1,startColorstr=#80000000, endColorstr=#80000000);
}
:root .bg{
    filter:none;/*IE9不需要filter*/
    background:#000;
    background: rgba(0, 0, 0,0.5);
}