<!doctype html>
<html>
<head>
  <style type="text/css">
    td {
      border: 1px solid black;
    }
  </style>
</head>
<body>
<table>
  <tr>
    <td>
	  <math>
	    <mspace width="50px" height="10px" mathbackground="green"/>
	  </math>
	</td>
    <td>
	  <math>
	    <mspace style="width: 100px;" width="50px" height="10px" mathbackground="green"/>
	  </math>
	</td>
    <td>
	  <math>
	    <mspace style="width: 10px;" width="50px" height="10px" mathbackground="green"/>
	  </math>
	</td>
  </tr>
</table>
</body>
</html>