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                            /HTML/CSS
                        
                        /如何用CSS进行网页布局

footer加入clear:both后，当浏览器宽度小于960px时，为什么footer右侧还是会露出body背景色？如何解决？

<!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>混合布局</title>
<style>
body{ margin:0; padding:0; font-size:30px; font-weight:bold;background-color: red;}
div{ text-align:center; line-height:50px}
.top{ height:100px;background:#9CF}
.head,.main{ width:960px; /*【任务1】*/margin:0 auto;}
.head{ height:100px; background:#F90}
.left{ width:220px; height:600px; background:#ccc; /*【任务2】*/float:left;}
.right{ width:740px; height:600px;background:#FCC; float:right}
.r_sub_left{ width:540px; height:600px; background:#9C3; float:left}
.r_sub_right{ width:200px; height:600px; background:#9FC; /*【任务3】*/float:right;}
.footer{ height:50px; background:#9F9; /*【任务4】*/clear:both;}
</style>
</head>

<body>
<div class="top">
    <div class="head">head</div>
</div>
<div class="main">
    <div class="left">left</div>
    <div class="right">
        <div class="r_sub_left">sub_left
        </div>
        <div class=" r_sub_right">sub_right
        </div>
    </div>
</div>
<div class="footer">footer</div>
</body>
</html>

设置body背景色为红色后，调小宽度可看到右下角的红色。