为什么“box6”里的“margin-top:10px”没有效果？
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<style type="text/css">
*{
margin:0;
padding:0;
font-family:"微软雅黑";
font-size:14px;
}
.wrap{
width:1000px;
margin:0 auto;
background:#FFF;
}
.box1{
width:100%;
height:80px;
}
.box1_left{
float:left;
}
.box1_right ul li a{
width:80px;
height:80px;
display:block;
text-align:center;
}
.box1_right li{
list-style-type:none;
float:left;
line-height:80px;
padding:0 20px;
}
.box1_right a:link,.box1_right a:visited{
text-decoration:none;
font-size:12px;
color:#333;
}
.box1_right a:hover,.box1_right a:active{
text-decoration:none;
background-color:#C33;}
.box2{
height:310px;
overflow:hidden;
margin:5px auto;
}
.box3{
width:100%;
height:30px;
margin-top:10px;}
.box3_left{
width:200px;
height:30px;
float:left;
background:#933;
text-align:center;
}
.box3_right{
width:800px;
height:30px;
float:left;
background:#333;
}
.box3 a:link,.box3 a:visited{
line-height:30px;
text-decoration:none;
color:#FFF;
}
.box3_right a{
margin-left:20px;
}
.box4_left,.box4_mid,.box4_right{
float:left;
}
.box4_mid{
margin:0 5px;
}
.box4{
width:100%;
height:100px;
margin-top:10px;
}
.box5{
width:100%;
height:20px;
}
.box5_left,.box5_mid,.box5_right{
float:left;
border:1px solid #CCC;
width:328px;
text-align:center;
line-height:20px;
}
.box5_mid{
margin:0 5px;
}
.box5 a:link,.box5 a:visited{
color:#333;
text-decoration:none;
font-size:10px;
}
.box6{
width:100%;
height:30px;
margin-top:10px;
}
.box6_left,.box6_mid,.box6_right{
width:330px;
line-height:30px;
float:left;
background-color:#933;
}
.box6_mid{
margin:0 5px;
}
.box6 a:link,.box6 a:visited{
text-decoration:none;
color:#FFF;
padding-left:20px;
font-size:10px;
}
</style>
</head>
<body>
<div class="wrap">
<div class="box1">
<div class="box1_left">
<img src="http://img1.sycdn.imooc.com//53edadad0001efe202000070.jpg" />
</div><!--box1_left结束-->
<div class="box1_right">
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<li><a href="#">帮助中心</a></li>
<li><a href="#">关于我们</a></li>
</ul>
</div><!--box1_right结束-->
</div><!--box1结束-->
<div class="box2" id="picBox">
<div class="loading"><img src="http://img1.sycdn.imooc.com//53edad8c000175cb00300029.jpg" alt="图片加载中" /></div>
<div class="pic">
<ul>
<li><img src="http://img1.sycdn.imooc.com//53edad3e0001afad10000318.jpg"</li>
<li><img src="http://img1.sycdn.imooc.com//53edad2c0001b61310000314.jpg"</li>
<li><img src="http://img1.sycdn.imooc.com//53edad1600019ae910000310.jpg"</li>
</ul>
</div>
</div><!--box2结束-->
<div class="box3">
<div class="box3_left"><a href="#">滚动新闻</a></div>
<div class="box3_right"><a href="#">这是滚动新闻</a></div>
</div><!--box3结束-->
<div class="box4">
<div class="box4_left"><img src="http://img1.sycdn.imooc.com//53edad54000119fb03300130.jpg" /></div>
<div class="box4_mid"><img src="http://img1.sycdn.imooc.com//53edad690001260a03300130.jpg" /></div>
<div class="box4_right"><img src="http://img1.sycdn.imooc.com//53edad7a0001cde803300130.jpg" /></div>
</div><!--box4结束-->
<div class="box5">
<div class="box5_left"><a href="#">玩转Bootstrap</a></div>
<div class="box5_mid"><a href="#">企业网站案例</a></div>
<div class="box5_right"><a href="#">Javascript基础</a></div>
</div><!--box5结束-->
<div class="box6">
<div class="box6_left"><a href="#">新闻中心</a></div>
<div class="box6_mid"><a href="#">热门活动</a></div>
<div class="box6_right"><a href="#">联系我们</a></div>
</div>
</div><!--wrap结束-->
</body>
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