code: public void injectUniqueCSS(String cssContent, String wrapperClass)
    {
      if(alreadyAddedCSS == null)
      {
        alreadyAddedCSS = new TreeSet<String>(); 
      }
      
      if(wrapperClass != null)
      {
        cssContent = wrapCSS(cssContent, wrapperClass);
      }
      
      String hashForCssContent = Hashing.md5().hashString(cssContent, Charsets.UTF_8).toString();
      if(!alreadyAddedCSS.contains(hashForCssContent))
      {
  //      CSSInject cssInject = new CSSInject(UI.getCurrent());
  //      cssInject.setStyles(cssContent);
        Page.getCurrent().getStyles().add(cssContent);
        alreadyAddedCSS.add(hashForCssContent);
      }
    }
docs: Inject CSS into the UI.
  This function will not add multiple style-elements if the
  exact CSS string was already added.
  @param cssContent
  @param wrapperClass Name of the wrapper class (a CSS class that is applied to a parent element)