为什么显示不出margin？
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
<style type="text/css">
img {margin:10px 18px;}
</style>
</head>
<body>
<img src="网页布局基础/case2/images/book1.jpg" width="80"height="80"/>
<img src="网页布局基础/case2/images/book2.jpg" width="80"height="80"/>
<img src="网页布局基础/case2/images/book3.jpg" width="80"height="80"/>
<img src="网页布局基础/case2/images/book4.jpg" width="80"height="80"/>
<img src="网页布局基础/case2/images/book5.jpg" width="80"height="80"/>
</body>
</html>
为什么显示不出margin？
