css/css-scroll-anchoring/negative-layout-overflow.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>

body {
  height: 1200px;
}
#header {
  position: relative;
  height: 100px;
}
#evil {
  position: relative;
  top: -900px;
  height: 1000px;
  width: 100px;
}
#changer {
  height: 100px;
}
#anchor {
  height: 100px;
  background-color: green;
}

</style>
<div id="header">
  <div id="evil"></div>
</div>
<div id="changer"></div>
<div id="anchor"></div>
<script>

// Tests that the anchor selection algorithm correctly accounts for negative
// positioning when computing bounds for visibility.

test(() => {
  document.scrollingElement.scrollTop = 250;
  document.querySelector("#changer").style.height = "200px";
  assert_equals(document.scrollingElement.scrollTop, 350);
}, "Anchor selection accounts for negative positioning.");

</script>