<!DOCTYPE html>
<meta charset=UTF-8>
<title>CSS Filter: Establishing containing block for absolutely-positioned elements, on an inline element</title>
<link rel="author" title="L. David Baron" href="https://dbaron.org/">
<link rel="author" title="Mozilla Corporation" href="http://mozilla.com/">
<style>
#cb {
position: relative;
filter: brightness(100%);
}
#abspos {
position: absolute;
top: 0;
left: 0;
width: 10px;
height: 10px;
background: blue;
}
</style>
<p>Filler text.</p>
<div>
<span id="cb">Blue box should cover top-left corner of this sentence.<span id="abspos"></span></span>
</div>