background.html

<!DOCTYPE html>
<html>
  <head>
  </head>
  <body>
    <script>
      /**
       * Fetch the f7u12 subreddit CSS
       */
      function fetchRageCSS(callback) {
        //This points to the f7u12 CSS file
        var cssLive = "http://www.reddit.com/r/fffffffuuuuuuuuuuuu/stylesheet.css"
        
        var xhr = new XMLHttpRequest();
        xhr.onreadystatechange = function(data) {
          if (xhr.readyState == 4) {
            if (xhr.status == 200) {
              callback(xhr.responseText);
            } else {
              callback(null);
            }
          }
        }
        
        xhr.open('GET', cssLive, true);
        xhr.send();
      };

      /**
       * Handles data sent via chrome.extension.sendRequest().
       * @param request Object Data sent in the request.
       * @param sender Object Origin of the request.
       * @param callback Function The method to call when the request completes.
       */
      function onRequest(request, sender, callback) {
        if (request.action == 'fetchRageCSS') {
          fetchRageCSS(callback);
        }
      };

      // Wire up the listener.
      chrome.extension.onRequest.addListener(onRequest);
    </script>
  </body>
</html>