<svg xmlns="http://www.w3.org/2000/svg" height="200" width="400">
 <style type="text/css">
  .fail { fill: red; }
  .pass { fill: green; }
 </style>
 <g class="fail"><rect x="0" y="0" width="400" height="200"/></g>
 <script type="text/javascript">
  document.getElementsByTagNameNS('http://www.w3.org/2000/svg', 'g')[0].setAttribute('class', 'pass');
 </script>
</svg>