<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <title>'em' widths</title>
  <style type="text/css">
   p { color: navy; }
   div { margin: 1em 0; height: 40px; width: 10em; background: navy; }
  </style>
 </head>
 <body>
  <p>There should be two identical bars below.</p>
  <p>First bar:</p>
  <div></div>
  <p>Second bar:</p>
  <svg preserveAspectRatio="none" height="40px" width="10em" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
   <rect x="0" y="0" width="100" height="100" fill="navy"/>
  </svg>
 </body>
</html>