ID选择器
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>浮动模型</title>
<style type="text/css">
div{
border:2px red solid;
width:200px;
height:400px;
}
#div1{float:left;}
#div2{float:right;}
</style>
</head>
<body>
<div id="div1"></div>
<div id="div2"></div>
</body>
</html>
问题是ID选择器不是只能写一次吗?为什么能写两次?