transform-box-will-change-transform-layer.html

<!doctype html>
<html class="reftest-wait">
<meta charset="utf-8">
<title>Verify transform-box animations on a 'will-change: transform' layer</title>
<link rel="match" href="transform-box-ref.html">
<link rel="help" href="https://drafts.csswg.org/css-transforms-2/#ctm">
<script src="/common/reftest-wait.js"></script>
<style>
  .block {
    position: absolute;
    border: 20px solid black;
    width: 100px;
    height: 100px;
    left: 100px;
    top: 100px;
    will-change: transform;
  }

  #transformBoxTarget {
    transform: rotateZ(90deg);
    transform-origin: 0% 100%;
    transform-box: border-box;
  }
</style>
<body>
  <div id="transformBoxTarget" class="block"></div>

<script>
  'use strict';

  async function waitForNextFrame() {
    return new Promise(resolve => {
      window.requestAnimationFrame(() => {
        resolve();
      });
    });
  }

  async function createAnimation(elementName, keyframes) {
    const element = document.getElementById(elementName);
    const anim = element.animate(keyframes, {
      duration: 1000,
      easing: 'linear',
      fill: 'forwards',
    });
    anim.pause();
    anim.currentTime = 2000;
    return anim.ready;
  }

  onload = async function() {
    await waitForNextFrame();
    await createAnimation('transformBoxTarget', [
        { transformBox: 'border-box',  borderColor: 'black' },
        { transformBox: 'content-box', borderColor: 'green' }]);

    await waitForNextFrame();
    takeScreenshot();
  };
</script>
</body>

chromium/third_party/blink/web_tests/external/wpt/css/css-transforms/animation/transform-box-will-change-transform-layer.html