it's simple only you have do is to give
background: rgba(0,0,0,0.3)
& for IE use this filter
background: transparent;
zoom: 1;
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#4C000000,endColorstr=#4C000000); /* IE 6 & 7 */
-ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#4C000000,endColorstr=#4C000000)"; /* IE8 */
you can generate your rgba filter from here http://kimili.com/journal/rgba-hsla-css-generator-for-internet-explorer/