CSS opacity

.transparent_class {
/* IE 8 */
-ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";

/* IE 5-7 */
filter: alpha(opacity=50);

/* Netscape */
-moz-opacity: 0.5;

/* Safari 1.x */
-khtml-opacity: 0.5;

/* Good browsers */
opacity: 0.5;
}