c's's透明度

alpha(opacity=70); opacity: 0.7;

背景透明

.transparent_class {  

      filter:alpha(opacity=50);  

     -moz-opacity:0.5;  

      -khtml-opacity: 0.5;  

      opacity: 0.5;  

}  

border透明

0;
height: 0;
display: block;
border: 25px;
border-style: solid;
border-color: #ccc transparent transparent transparent;