<!DOCTYPE html>
<style>
#backdrop {
    position: absolute;
    top: 100px;
    left: 100px;
    height: 100px;
    width: 100px;
    background: green;
}
</style>
<body>
Test that position 'static' or 'relative' for ::backdrop computes to 'absolute'.
The test passes if there is a single green box.
<div id="backdrop"></div>
</body>
