code: function(id, url) {
              var ss;
              CSS.removeStyleSheet(id);
              ss = doc.createElement("link");
              ss.setAttribute("rel", "stylesheet");
              ss.setAttribute("type", "text/css");
              ss.setAttribute("id", id);
              ss.setAttribute("href", url);
              doc.getElementsByTagName("head")[0].appendChild(ss);
          }
docs: Dynamically swaps an existing stylesheet reference for a new one
  @param {String} id The id of an existing link tag to remove
  @param {String} url The href of the new stylesheet to include