1.opacity:0.5;(半透明效果在ie9及以上版本适用，ie8及以下不兼容)
解决办法：在css中加入filter: progid:DXImageTransform.Microsoft.Alpha(opacity=50);即可
eg: .fb_xl li{
font-size:16px; color:#FFF; 230px; line-height:35px;
background:#66cc97 center repeat; opacity:0.5; list-style:none; z-index: 9999;
filter: progid:DXImageTransform.Microsoft.Alpha(opacity=50);
}