DIV背景透明样式代码：
.alert{filter:alpha(opacity=100);
/*IE*/-moz-opacity:1.0;/*Moz+FF*/
opacity:1.0;height:300px;width:500px;
background:#ccc;left:50%;top:50%;margin-top:-150px;
margin-left:-250px;position:absolute;z-index:99;
text-align:center;padding:20px;}
使用方法：
<divclassdivclass=”alert”> DIV背景透明 </div>
html代码：
<!DOCTYPEhtmlPUBLIC"-//W3C//DTDXHTML1.0Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<htmlxmlnshtmlxmlns="http://www.w3.org/1999/xhtml">
<head>
<metahttp-
equiv="Content-Type"content="text/html;charset=utf-8"/>
<title>jqueryajax.com--jquery学习资料</title>
<styletypestyletype="text/css">
.alert
{filter:alpha(opacity=100);/*IE*/-moz-opacity:1.0;
/*Moz+FF*/opacity:1.0;height:300px;
width:500px;background:#ccc;left:50%;top:50%;
margin-top:-150px;margin-left:
-250px;position:absolute;z-index:99;
text-align:center;padding:20px}
</style>
</head>
<body>
<divclassdivclass="alert">DIV背景透明
</div>
</body>
</html>