<!DOCTYPE HTML>
<style>
    body {
        margin: 0;
    }
    #container {
        position: relative;
        top: 40px;
        width: 200px;
        height: 400px;
    }
    #test {
        position: absolute;
        background-color: green;
        width: 100px;
        height: 100px;
        margin-top: 20px;
    }
</style>
<div id="container">
    <div id="test"></div>
</div>
Tests the repainting of absolute element when margin-top changes.