<!DOCTYPE html>
<!--
 | Relative positioned elements should be placed in the correct stacking
 | context, even when their containing block is nearer and is an in-flow,
 | non-positioned descendants The results should show the blue box in front of
 | the green box.
 |   https://www.w3.org/TR/CSS21/visuren.html#z-index
 -->
<html>
<head>
  <style>
    .container {
      position: absolute;

      width: 150px;
      height: 150px;

      background-color: rgb(158, 158, 158);
    }
    .green {
      position: absolute;

      left: 0px;
      top: 0px;

      width: 80px;
      height: 80px;

      background-color: rgb(15, 157, 88);
    }
    .blue-container {
      position: static;

      left: 20px;
      top: 20px;

      width: 150px;
      height: 150px;
    }
    .blue {
      position: relative;

      left: 40px;
      top: 40px;

      width: 80px;
      height: 80px;

      background-color: rgb(66, 133, 244);
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="green"></div>
    <div class="blue-container">
      <div class="blue"></div>
    </div>
  </div>
</body>
</html>