html文件：
<html>
<head><title>test</title>
<link href="mm.css" rel="stylesheet" type="text/css"/>
</head>
<body>
<div class="mm">
</div>
<div class="gg">
</div>
<div class="qiuqiu">
</div>
</body>
</html>
css文件：
.mm,.gg,.qiuqiu{
margin:0px;
padding:0px;
990px;
height:180px;
}
.mm{
background-color:#FF00FF;
}
.gg{
background-color:#FFFF00;
}
.qiuqiu{
background-color:#dfdfdf;
}