fune/testing/web-platform/tests/css/css-scroll-anchoring/fragment-scrolling-anchors.html

<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring/">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  body {
    margin: 0px;
    height: 2000px;
    width: 2000px;
  }

  #first {
    height: 1000px;
    background-color: #FFA5D2;
  }

  #anchor {
    position: absolute;
    background-color: #84BE6A;
    height: 600px;
    width: 100%;
  }

  #fragment {
    position: relative;
    background-color: orange;
    height: 200px;
    width: 200px;
    margin: 10px;
  }
</style>

<div id="first"></div>
<div id="changer"></div>
<div id="anchor">
    <div id="fragment" name="fragment"></div>
</div>

<script>
  promise_test(async function(t) {
    // Note that this test passes even without scroll anchoring because of
    // fragment anchoring.
    window.location.hash = 'fragment';
    // Height of first + fragment margin-top.
    assert_equals(window.scrollY, 1010);

    // Change height of content above fragment.
    var ch = document.getElementById('changer');
    ch.style.height = 100;

    await new Promise(resolve => addEventListener('scroll', resolve, {once: true}));

    // Height of first + height changer + fragment margin-top.
    assert_equals(window.scrollY, 1110);

    first.remove();
    changer.remove();
    anchor.remove();
  }, 'Verify scroll anchoring interaction with fragment scrolls');
</script>