<!DOCTYPE html>
<!--
 | Setting an absolute positioned element's height to a percentage value should
 | result in computed height remaining a percentage and the used value being
 | a percentage height of the containing block.
 -->
<html>
<head>
  <style>
    body {
      margin: 0;
    }

    .expand {
      position: absolute;
      background-color: rgb(255, 100, 100);
      width:100px;
      height:75%;
    }
  </style>
</head>
<body>
  <div>
    <div class="expand">
    </div>
  </div>
</body>
</html>