<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>position_absolute</title>
<style>
.div1{
background-color: #2eb1fc;
100px;
height:100px;
}
.div2{
background-color:#1ecc86;
100px;
height:100px;
position:absolute;
/*absolute会向上寻找他的父级（直到position的值不为None），如果找不到则会一直向上找*/
/*此处div2出现这种情况，是因为他的父级class='box_2'的position为None，所以它的位置相对外部的html移动，所以图形才会变成这样*/
/*解决方法：*/
/*给父级position加上非空属性值*/
/*if the element has 'position:absolute',the containing block is established by the nearest ancester*/
/*with a'position' of 'absolute' ,'ralative' or 'fixed'.*/
left:100px;
top:100px;
}
.div3{
background-color:#71a403;
200px;
height:200px;
}
.box_2{
position:relative;
border:3px solid rebeccapurple;
}
</style>
</head>
<body>
<div class="div1">111</div>
<div class="box_2">
<div class="div2">222</div>
</div>
<div class="div3">333</div>
</body>
</html>