<!DOCTYPE html> <meta charset="utf-8"> <title>CSS will-change: 'will-change: height' does not create a containing block for fixed positioned elements</title> <link rel="author" title="L. David Baron" href="https://dbaron.org/"> <link rel="author" title="Mozilla" href="http://www.mozilla.org/"> <link rel="help" href="https://drafts.csswg.org/css-will-change-1/#will-change"> <link rel="match" href="green-square-100-by-100-offset-ref.html"> <meta name="assert" content="If any non-initial value of a property would cause the element to generate a containing block for fixed-position elements, specifying that property in will-change must cause the element to generate a containing block for fixed-position elements."> <style> html, body { margin: 0; padding: 0; } div { width: 100px; height: 100px } #wc { will-change: height; margin: 100px 0 0 100px; background: red } .child { top: 100px; left: 100px; width: 50px; background: green } #fixpos { position: fixed } #abspos { position: absolute; left: 150px } </style> <body> <div id="wc"> <div class="child" id="fixpos"> </div> <div class="child" id="abspos"> </div> </div> </body>