scroll-animations/css/progress-based-animation-timeline.html

<!DOCTYPE html>
<title>CSS Animation using progress based timeline</title>
<link rel="help" src="https://drafts.csswg.org/css-animations-2/#animation-timeline">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<style>
  #scrollers {
    overflow: hidden;
    height: 0px;
  }
  #scrollers > div {
    overflow: scroll;
    width: 100px;
    height: 100px;
  }
  #scrollers > div > div {
    height: 200px;
  }

  @keyframes top {
    from { top: 100px; }
    to { top: 200px; }
  }

  @scroll-timeline top_timeline {
    source: selector(#scroller1);
    start: 0px;
    end: 100px;
  }

  #element {
    animation-name: top;
    animation-duration: 10s;
    animation-timing-function: linear;
    animation-timeline: top_timeline;
  }
  /* Ensure stable expectations if feature is not supported */
  @supports not (animation-timeline:foo) {
    #element { animation-play-state: paused; }
  }
</style>
<div id=scrollers>
  <div id=scroller1><div></div></div>
</div>
<div id=element></div>
<script>
  // Force layout of scrollers.
  scroller1.offsetTop;

  scroller1.scrollTop = 20;

  promise_test(async (t) => {
    await waitForNextFrame();
    assert_equals(getComputedStyle(element).top, '120px');
  }, 'progress based animation timeline works');

</script>