为什么son1看起来像是参照f2定位的?son1 距离页面顶端也有30px
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="utf-8">
<title>Test2</title>
<style type="text/css">
#f1 {
background-color: #b6ff00;
}
#son1 {
position: absolute;
background-color: green;
height:40px;
}
#f2 {
margin-top: 30px;
height: 161px;
background-color: red;
}
</style>
</head>
<body>
<div id="top">
<div id="f1">
<div id="son1">son1</div>
</div>
<div id="f2">
ddddddddddd
</div>
</div>
</body>
</html>