纯粹的CSS无法实现。因为position:absolute就是脱离文档流，怎么能让父元素不塌陷呢？ 目前想到的只能用js和jquery来实现了，用js获取子元素的高度，赋值给父元素。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1,user-scalable=0">
<title>test</title>
</head>
<style>
.out {
position:relative;
}
.out:after{
content: "";
clear: both;
}
.inner {
position:absolute;
height:60px;
background-color:#afe;
width:100%;
}
</style>
<body>
<h1>父元素的高度崩塌</h1>
<div class="out">
<div class="inner">
</div>
</div> <script> window.onload=function(){
var h = document.getElementsByClassName("inner")[0].offsetHeight;
console.log(h);
document.getElementsByClassName("out")[0].style.height = h + 'px'; } </script>
</body>
</html>
jquery写法：