<!DOCTYPE html>
<title>The animation-timeline: scroll-timeline-name</title>
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timelines-named">
<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/6674">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<script src="support/testcommon.js"></script>
<style>
  @keyframes grow-progress {
    to { width: 300px; }
  }

  .scrollcontainer {
    overflow-x: scroll;
    display: flex;
    flex-direction: row;
    scroll-timeline:  --timeline inline;
  }

  .progress {
    position: absolute;
    z-index: 10;
    left: 0;
    top: 0;
    width: 100px;
    height: 1em;
    background: red;
    animation: auto grow-progress linear forwards;
    animation-timeline: scroll(inline nearest);
  }

  .entry {
    min-height:  90vh;
    min-width: 100vw;
  }

  .entry:nth-child(even) {
    background-color:  #eee;
  }

  .entry:nth-child(odd) {
   background-color:  #ddd;
  }
</style>
<body>
  <div class = "scrollcontainer" id = "scroller">
    <div class = "progress" id = "target"></div>
    <div class = "entry"></div>
    <div class = "entry"></div>
    <div class = "entry"></div>
  </div>
</body>
<script>
"use strict";

setup(assert_implements_animation_timeline);

promise_test(async t => {
  const maxScroll = scroller.scrollWidth - scroller.clientWidth;
  scroller.scrollLeft = maxScroll;

  // Advance to next frame so that scroll-timeline has a valid time.
  await waitForNextFrame();

  // Flex container is not position relative and therefore not the container for
  // the progress element.
  assert_equals(getComputedStyle(target).width, "100px");

  // Once the scroller is position relative, it becomes the container block for
  // the progress element.
  scroller.style.position = 'relative';
  await waitForNextFrame();

  assert_equals(getComputedStyle(target).width, "300px");
}, 'Resolving scroll(nearest) for an absolutely positioned element');

</script>
