chromium/third_party/blink/web_tests/fast/multicol/change-column-rule.html

<!DOCTYPE html>
<p>The rules below should be green, and there should be no assertion failures.</p>
<div id="mc" style="columns:3; line-height:100px; column-rule:solid yellow;">
    <br>
    <br>
    <br>
</div>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<script>
runAfterLayoutAndPaint(function() {
  mc.style.webkitColumnRuleColor = 'green';
}, true);
</script>