在html文件里写style样式可以显示，但是放到外面的css文件中，然后想link进来，就没用，请问是什么问题？
<!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>电商网站</title>
//<link href="style/main.css" rel="stylesheet" type="text/css" />
<style type="text/css">
.comwidth{width:1000px; margin-left:auto; margin-right:auto;}
.topbar{heigt:31px; background-color:#0000ff;}
</style>
</head>
<body>
<div class="headbar" >
<div class="topbar">
<div class="comwidth">
<div class="lefttop" >
<a href="#" class="collection">收藏</a>
</div>
<div class="righttop" >
登录
</div>
</div>
</div>
<div class="logobar">
<div class="comwidth">
<div class="logo">
<a href="#" > <img src="#" alt="慕课网" /></a>
</div>
<div class="searchbox">
<input type="text" class="searchtext" />
<input type="button" class="searchbutton" value="搜索" />
</div>
<div class="shopcar">
<span class="shoptext">购物车</span>
<span class="shopnum">0</span>
</div>
</div>
</div>
<div class="buttonbar">
<div class="comwidth">
<div class="shopclass">
<h3>全部商品分类</h3>
</div>
<ul class="nav">
<li><a href="#">数码城</a> </li>
<li><a href="#">天黑黑</a> </li>
<li><a href="#">团购</a> </li>
<li><a href="#">发现</a> </li>
<li><a href="#">二手特卖</a> </li>
<li><a href="#">名品会</a> </li>
</ul>
</div>
</div>
</div>
</body>
</html>
