<!doctype html>
<html>
  <head>
    <title>testcase</title>
    <meta charset="utf-8"/>
    <style type="text/css">
      body {
      overflow: hidden;
      }
    </style>
  </head>
  <body>

    <div style="position: absolute; top: 1em; left: 0; width: 100%;">
      <div style="position: absolute; top: -2px; left: -2px; width: 100%;
                  border: 2px solid green; background: red;">
        <math style="visibility: hidden;">
          <msqrt>
            <mi>x</mi>
            <mi>y</mi>
          </msqrt>
        </math>
      </div>
    </div>

    <div style="position: absolute; top: 5em; left: 0; width: 100%;">
      <div style="position: absolute; top: -2px; left: -2px; width: 100%;
                  border: 2px solid green; background: blue;">
        <math style="visibility: hidden;">
          <msup>
            <mi>x</mi>
            <mi>y</mi>
          </msup>
        </math>
      </div>
    </div>

  </body>
</html>