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chromium/third_party/blink/web_tests/external/wpt/css/css-position/position-change-ref.html 

<!doctype HTML>
<title>CSS Test Reference</title>
<div style="position: relative; background: red; width: 100px; height: 100px; overflow: hidden;">
  <div style="overflow-y: scroll; width: 400px; height: 400px;">
    <div style="height: 100px; width: 100px; background: green;"></div>
    <!-- forces scrolling -->
    <div style="height: 700px;"></div>
  </div>
</div>