浮动模型中,div1{margin-left:10px}和div2{margin-right :10px},为什么两个div之间间距是20px而不是10px？
<!DOCTYPE HTML>
<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:160px;
height:400px;
float:left;
}
#div1{margin-right:10px;}
#div2{margin-left:10px;}
</style>
</head>
<body>
<div id="div1">栏目1</div>
<div id="div2">栏目2</div>
</body>
</html>
