css rgba透明度变化

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <title>无标题文档</title>
 <style type="text/css">
 li[class^="rgba"]{
     float:left;
     width:100px;
     height:80px;
     border:#CCC solid 1px;
     text-align:center;
     font-size:12px;
 }
 li[class*="1"]{background:rgba(255,0,0,0.1);}
 li[class*="2"]{background:rgba(255,0,0,0.3);}
 li[class*="3"]{background:rgba(255,0,0,0.5);}
 li[class*="4"]{background:rgba(255,0,0,0.7);}
 li[class*="5"]{background:rgba(255,0,0,0.9);}
 </style>

 </head>

 <body>
 <li class="rgba1">你好</li>
 <li class="rgba2">你好</li>
 <li class="rgba3">你好</li>
 <li class="rgba4">你好</li>
 <li class="rgba5">你好</li>
 </body>
 </html>