<!DOCTYPE html>
<style>
#container {
    position: fixed;
    top: 200px;
    left: 100px;
}

#block {
    position: relative;
    width: 100px;
    height: 100px;
    top: 50px;
    background-color: green;
}
</style>
<div id="container">
    <div id="block"></div>
</div>
This test passes if the green block stays at the same place after repaint.