chromium/third_party/blink/web_tests/wpt_internal/css/css-anchor-position-inset-area-old/inset-area-scroll-adjust.html

<!DOCTYPE html>
<title>CSS Anchor Positioning: inset-area anchored against scrolling anchor</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position/#inset-area">
<link rel="match" href="inset-area-scroll-adjust-ref.html">
<style>
  #scroller {
    width: 400px;
    height: 200px;
    overflow: auto;
  }
  #anchor {
    background: green;
    width: 200px;
    height: 100px;
  }
  #anchored {
    inset-area: bottom;
    margin: 0;
    padding: 0;
    border: none;
    background: green;
    width: 200px;
    height: 100px;
  }
  .filler { height: 200px; }
</style>
<p>You should see a green square below</p>
<div id="scroller">
  <div class="filler"></div>
  <div id="anchor" popovertarget="anchored"></div>
  <div id="anchored" anchor="anchor" popover></div>
  <div class="filler"></div>
  <div class="filler"></div>
</div>
<script>
  anchored.showPopover();
  scroller.scrollTop = 200;
</script>