半透明，记一笔

原文出处：http://justgeeks.blogspot.com/2009/06/controlling-opacity-of-background-color.html 

.mySemitransparentBackground { 

background-color: #fff; 

filter:progid:DXImageTransform.Microsoft.alpha(opacity=50); 

opacity: 0.5; 

height:500px;

500px;

}