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chromium/third_party/blink/web_tests/external/wpt/fullscreen/rendering/backdrop-object-ref.html 

<!DOCTYPE html>
<style>
body {
    background: blue;
    margin: 0;
}
div {
    position: fixed;
    width: 100px;
    height: 100px;
    background: green;
}
</style>
<div></div>