chromium/third_party/blink/web_tests/compositing/overflow/fixed-position-ancestor-clip.html

<!DOCTYPE>

<html>
<head>
  <title>Position fixed with transform</title>
  <style type="text/css" media="screen">
    ::-webkit-scrollbar {
      width: 0px;
      height: 0px;
    }
    body {
      height: 1000px;
      width: 1000px;
    }
    #fixed {
      position: fixed;
      width: 100px;
      height: 100px;
      background-color: red;
      overflow: hidden;
    }
    
    .box {
      width: 100px;
      height: 100px;
      background-color: green;
      will-change: transform;
    }

    p {
      position: absolute;
      left: 50px;
      top: 150px;
    }
  </style>
  <script type="text/javascript" charset="utf-8">
    window.addEventListener('load', function() {
      window.scrollBy(50, 50);
    }, false);
  </script>
</head>
<body>
  
  <p>You should see a single green square, with no red.</p>
  <div id="fixed">
    <div class="box">
    </div>
  </div>

</body>
</html>