<!DOCTYPE html>
<html>
<head>

<meta name="viewport" content="width=800">
<style>
html { font-size: 16px; }
body { width: 800px; overflow-y: hidden; }
</style>

</head>
<body>

<div style="width: 400px">
  <div style="font-size: 1.25rem">
    This text should be autosized to just 20px computed font size (16 * 400/320), since the width of the least common ancestor of the cluster's text descendants is used for multiplier calculation.
  </div>

  <div style="font-size: 1.25rem">
    This text should be similarly autosized to 20px.
  </div>
</div>
</body>
</html>