元素透明_IE_FF_Sar_Op_Cho

pre {                               /* make the box translucent (80% opaque) */ 
   border: solid red; 
   opacity: 0.8;                    /* Firefox, Safari(WebKit), Opera */ 
   -ms-filter: "alpha(opacity=80)"; /* IE 8 */ 
   filter: alpha(opacity=80);       /* IE 4-7 */ 
   zoom: 1;       /* set "zoom", "width" or "height" to trigger "hasLayout" in IE 7 and lower */  
} 

ref:https://developer.mozilla.org/En/CSS:-moz-opacity