<!DOCTYPE html>
<!--
 | Stacking contexts are different from containing blocks, and elements of
 | differing containing blocks can share the same stacking context.  This
 | test ensures that elements with differing containing blocks are rendered
 | in the correct order according to their mutual stacking context.
 | The results should show the blue box infront of all other boxes as it has
 | the largest z-index, even though it is a child of another element that does
 | not have z-index specified.  The gray box containing the blue box should
 | appear in the back as it has an implied z-index of 0.
 |   https://www.w3.org/TR/CSS21/visuren.html#z-index
 -->
<html>
<head>
  <style>
    .red, .green, .blue {
      position: absolute;
      width: 100px;
      height: 100px;
    }
    .red {
      left: 0px;
      top: 0px;
      background-color: rgb(255, 100, 100);
      z-index: 1;
    }
    .green {
      left: 30px;
      top: 30px;
      background-color: rgb(100, 255, 100);
      z-index: 2;
    }
    .blue {
      left: 40px;
      top: 40px;
      background-color: rgb(100, 100, 255);
      z-index: 3;
    }
    .blue-container {
      position: absolute;
      left: 20px;
      top: 20px;

      width: 150px;
      height: 150px;

      background-color: rgb(100, 100, 100);
    }
  </style>
</head>
<body>
  <div class="blue-container">
    <div class="blue"></div>
  </div>
  <div class="green"></div>
  <div class="red"></div>
</body>
</html>