animation-with-root-scroller-ref.html

<!DOCTYPE html>
<title>Reference for Scroll timeline with Web Animation using the root scroller</title>
<style>
  html {
    min-height: 100%;
    min-width: 100%;
    padding-bottom: 100px;
    padding-right: 100px;
  }

  #box {
    width: 100px;
    height: 100px;
    background-color: green;
    transform: translate(0, 100px);
    opacity: 0.5;
    will-change: transform; /* force compositing */
  }

  #covered {
    width: 100px;
    height: 100px;
    background-color: red;
  }
</style>

<div id="box"></div>
<div id="covered"><p>Covered Contents</p></div>

<script>
  window.addEventListener('load', function() {
    // Move the scroller to halfway.
    const scroller = document.scrollingElement;
    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
    scroller.scrollTop = 0.5 * maxScroll;
  });
</script>

chromium/third_party/blink/web_tests/external/wpt/scroll-animations/scroll-timelines/animation-with-root-scroller-ref.html