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chromium/third_party/blink/web_tests/paint/invalidation/multicol/multicol-rule-actual-columns-change-expected.html 

<!DOCTYPE html>
<div style="column-fill: auto; columns: 4; column-rule: 10px solid blue; width: 400px; height: 400px">
  <div id="content" style="height: 1000px; background: gray"></div>
</div>