css/css-contain/contain-layout-018.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Containment Test: Layout containment stacking context</title>
<link rel="author" title="Manuel Rego Casasnovas" href="mailto:rego@igalia.com">
<link rel="help" href="https://drafts.csswg.org/css-contain-1/#containment-layout">
<link rel="match" href="../reference/nothing.html">
<meta name=assert content="Elements in which layout containment doesn't apply, do not create a stacking context.">
<style>
div {
  display: inline;
  contain: layout;
  background: white;
}
span {
  position: relative;
  z-index: -1;
}
</style>

<p>There should be nothing below.</p>
<div><span>FAIL</span></div>