css/css-contain/contain-layout-independent-formatting-context-001.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS Containment Test: Layout containment independent formatting 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/contain-paint-independent-formatting-context-001-ref.html">
<meta name=assert content="Layout containment elements establish an independent formatting context. The test checks that this feature of layout containment applies to blocks.">
<style>
.wrapper {
  border: solid thick;
  margin: 1em;
}
</style>
<p>Test passes if it has the same output than the reference.</p>
<div class="wrapper">
  <div style="margin: 1em 0; contain: layout;">
    <div style="margin: 1em 0;">This text should have 2em top and bottom margins (margins do not collapse).</div>
  </div>
</div>