<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8"/>
    <title>fraction rendering from in-flow children</title>
  </head>
  <body>
    <math>
      <mfrac>
        <mspace width="64px" height="48px" style="background: lightblue"></mspace>
        <mspace width="128px" height="96px" style="background: lightgreen"></mspace>
      </mfrac>
    </math>
  </body>
</html>