<!DOCTYPE html>

<html>
<head>
  <style>
    body {
      margin: 0;
      height: 1000px;
    }
    
    body > div {
      outline: 1px solid black;
    }
    
    .box {
      width: 100px;
      height: 100px;
    }

    .fixed {
      position: fixed;
      top: 100px;
      background-color: green;
    }

    .perspective {
      -webkit-perspective: 500px;
    }

    .transformed {
      -webkit-transform: translateZ(1px);
    }
  </style>
  <script>
    // Scroll on load to test fixed positioning.
    window.addEventListener('load', function() {
      window.scrollTo(0, 100);
    }, false)
  </script>
</head>
<body>

  <div class="perspective box" style="margin: 150px 50px;">
    <div class="fixed box">
        <div class="transformed box"></div> <!-- Necessary to activate preserve3d compositing -->
    </div>
  </div>

  <div class="perspective fixed box" style="left: 250px;">
    <div class="transformed box"></div> <!-- Necessary to activate preserve3d compositing -->
  </div>
</body>
</html>