background:#000;
background:transparent;
filter:
progid:DXImageTransform.Microsoft.gradient(startColorstr=#aa000000,endColorstr=#aa000000);
/*
IE6,IE7 */
-ms-filter:
progid:DXImageTransform.Microsoft.gradient(startColorstr=#aa000000,endColorstr=#aa000000); /*ie8*/
background:rgba(0,
0, 0, 0.5); /*
FF3+, Saf3+, Opera 10.10+, Chrome */
原文：http://www.cnblogs.com/sencha/p/3532405.html