<!DOCTYPE html>
<title>CSS Animation using progress based timeline</title>
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
<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>
  main > div {
    overflow: hidden;
    width: 100px;
    height: 100px;
  }
  main > div > div {
    height: 200px;
  }

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

  #scroller1 {
    scroll-timeline: --top_timeline;
  }

  #element {
    animation-name: top;
    animation-duration: 10s;
    animation-timing-function: linear;
    animation-timeline: --top_timeline;
    position: absolute;
  }
  /* Ensure stable expectations if feature is not supported */
  @supports not (animation-timeline:--foo) {
    #element { animation-play-state: paused; }
  }
</style>
<main>
  <div id=scroller1>
    <div></div>
    <div id=element></div>
  </div>
</main>
<script>
  window.onload = async () => {
    promise_test(async (t) => {
      await waitForNextFrame();
      const anim = document.getAnimations()[0];
      await anim.ready;
      scroller1.scrollTop = 20;
      await waitForNextFrame();
      assert_equals(getComputedStyle(element).top, '120px');
    }, 'progress based animation timeline works');
  };
</script>
