chromium/third_party/blink/web_tests/css3/filters/filter-region.html

<!DOCTYPE html>

<html lang="en">
<head>
  <style>
    .box {
      position: absolute;
      height: 50px;
      width: 100px;
      left: 20px;
      background-color: green;
      outline: 4px solid black;
      filter: blur(0);
    }
    
    .indicator {
      top: 50px;
      background-color: red;
    }
  </style>
</head>
<body>

  <!-- You should see two green rectangles with black outlines, and no red. -->
  <div class="indicator box"></div>
  <div class="box">
    <div class="box" style="top: 50px; left: 0"></div>
  </div>

</body>
</html>