chromium/third_party/blink/web_tests/external/wpt/css/css-contain/contain-paint-dynamic-003.html

<!DOCTYPE html>
<html class="reftest-wait">
<meta charset="utf-8">
<title>Dynamic change to paint containment</title>
<link rel="help" href="https://drafts.csswg.org/css-contain/#contain-property">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1765615">
<meta name="assert" content="Verify paint containment is properly updated after dynamic change to the contain property.">
<link rel="match" href="contain-paint-dynamic-003-ref.html">

<script src="/common/reftest-wait.js"></script>
<script src="/common/rendering-utils.js"></script>

<style>
  #container {
      width: 100px;
      height: 100px;
      background: green;
      contain: paint;
  }
  #overflowing {
      width: 400px;
      height: 100px;
  }
  .square {
      display: inline-block;
      width: 50px;
      height: 50px;
      margin: 5px;
  }
  .green {
      background: green;
  }
</style>

<body>
  <p>PASS if you see <em>two</em> green squares.</p>
  <div id="container">
    <div id="overflowing"><div class="square"></div><div class="square"></div><div class="red square"></div></div>
  </div>
  <script>
    window.addEventListener("TestRendered", async () => {
        container.style.contain = "none";
        await waitForAtLeastOneFrame();
        takeScreenshot();
    });
  </script>
</body>
</html>