用CSS设定一个元素半透明

.opacity{  filter:alpha(opacity=50);       
/* IE */  -moz-opacity:0.5;              
/* 老版Mozilla */  -khtml-opacity:0.5;              
/* 老版Safari */  opacity: 0.5;           
/* 支持opacity的浏览器*/}

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

img{-ms-interpolation-mode: bicubic;}