<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS will-change: 'will-change: mask' creates a stacking context</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="help" href="http://www.w3.org/TR/css-masking/#the-mask-image">
<link rel="match" href="green-square-100-by-100-ref.html">
<meta name="assert" content="If any non-initial value of a property would create a stacking context on the element, specifying that property in will-change must create a stacking context on the element.">
<style>
html, body { margin: 0; padding: 0; }
div { width: 100px; height: 100px }
#wc { will-change: mask; background: red }
#child { position: absolute; top: 0; left: 0; z-index: -1; background: green }
</style>
<body>
  <div id="wc">
    <div id="child">
    </div>
  </div>
</body>