html调用类的问题
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>边框</title>
<style type="text/css">
.div1{margin:50px;border:1px solid red;padding:50px;}
div2{margin:5px;border:1px solid red;padding:5px;}
</style>
</head>
<body>
<div class="div1"><div calss="div2"></div>
</div>
</body>
</html>
为什么调用类div2的时候没边框，必须改成div{margin:5px;border:1px solid red;padding:5px;}或者div div才有用？关于容器调用类和元素调用类一直不明白
