chromium/third_party/blink/web_tests/external/wpt/css/css-anchor-position/position-visibility-anchors-valid-ref.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>
  .anchor {
    width: 100px;
    height: 100px;
    background: orange;
  }
  .target {
    width: 100px;
    height: 100px;
    background: green;
  }
</style>

<div class="anchor">anchor1</div>
<div class="target">target1</div>