为什么使用了overflow：hidden之后mainbody层还是被缩进去了？检查了很多遍都看不出来问题额
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>xiangmu2</title>
<style type="text/css" >
*{margin:0;padding:0;}
#wrap{
background-color:lightpink;
margin:0 auto;
width:960px;
}
#header{background-color:yellowgreen;
width:100%;}
#mainbody{
background-color:hotpink;
width:100%;
overflow:hidden;
}
.left{
width:800px;
height:300px;
background-color:darkred;
float:left;
}
.right{
width:140px;
height:500px;
background-color:black;
float:right;
}
#footer:{
background-color:paleturquoise;
width:100%;
}
</style>
</head>
<body>
<div id="wrap">
<div id="header">头部</div>
<div id="mainbody">主体内容</div>
<div class="left">56</div>
<div class="right">asdgahadha</div>
<div id="footer">版权部分</div>
</div>
</body>
</html>
