.opacity{
filter:alpha(opacity=50);
-moz-opacity:0.5;
-khtml-opacity:0.5;
opacity: 0.5;
}
用javascript来设定一个元素为半透明:
.object.filter = "alpha(opacity=" + opacity + ")";
.object.MozOpacity = (opacity / 100);
.object.KhtmlOpacity = (opacity / 100);
.object.opacity = (opacity / 100);
原文:http://www.cnblogs.com/xiashunjie/p/5160357.html