css/css-will-change/will-change-stacking-context-z-index-2.html

<!DOCTYPE html>
<title>CSS Test: `will-change: z-index`</title>
<link rel="author" title="Oriol Brufau" href="obrufau@igalia.com">
<link rel="help" href="https://www.w3.org/TR/css-will-change/#valdef-will-change-custom-ident">
<link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#painting">
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/11827">
<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
<meta name="assert" content="
  `will-change: z-index` establishes a stacking context on a flex item.
">
<style>
.test {
  will-change: z-index;
  width: 100px;
  background: red;
}
.test::before {
  content: "";
  display: block;
  position: relative;
  z-index: -1;
  height: 100px;
  background: green;
}
</style>
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div style="display: flex">
  <div class="test"></div>
</div>