<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#abs-pos {
position: absolute;
top: 20px; left: 20px;
width: 200px;
background-color: lightgreen;
}
#in-flow-child {
height: 100px;
margin-top: 40px;
margin-bottom: 40px;
background-color: green;
}
</style>
</head>
<body>
<div id="abs-pos">
<div id="in-flow-child"></div>
</div>
</body>
</html>