1 .opacity{
2     position: absolute;
3     top: 0px;left: 0px;
4     background: #000;
5     filter:alpha(opacity=50);       /* IE */
6     -moz-opacity:0.5;              /* 老版Mozilla */
7     -khtml-opacity:0.5;              /* 老版Safari */
8       opacity: 0.5;           /* 支持opacity的浏览器*/
9 }

1 object.filter = "alpha(opacity=" + opacity + ")";  /* IE */
2 object.MozOpacity = (opacity / 100);           /* 老版Mozilla */
3 object.KhtmlOpacity = (opacity / 100);           /* 老版Safari */
4 object.opacity = (opacity / 100);           /* 支持opacity的浏览器*/