getComputedStyle-sticky-pos-percent.html

<!DOCTYPE html>
<title>CSS Test: resolve top percentage value against proper box</title>
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/3115" />
<link rel="help" href="https://drafts.csswg.org/css-position/#sticky-pos" />
<link rel="help" href="https://drafts.csswg.org/cssom/#resolved-values" />
<meta name="assert" content="Test that the sticky percentage insets are
resolved against the right ancestor, i.e. the nearest scrollport." />

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<div style="height: 500px; background: purple; overflow: hidden;">
  <div style="height: 400px; background: yellow;">
    <div id="target" style="height: 100px; position: sticky; left: 0; top: 50%; background: blue;">
    </div>
  </div>
</div>
<script>
test(() => {
  assert_equals(getComputedStyle(target).top, '250px');
}, "Sticky element's top property percentage value should be resolved against the div with overflow: hidden");
</script>

chromium/third_party/blink/web_tests/external/wpt/css/cssom/getComputedStyle-sticky-pos-percent.html