code: private void hideLoadingPopup() {
          final Element e = RootPanel.get("loading").getElement();
  
          new Animation() {
  
              @Override
              protected void onUpdate( double progress ) {
                  e.getStyle().setOpacity( 1.0 - progress );
              }
  
              @Override
              protected void onComplete() {
                  e.getStyle().setVisibility( Style.Visibility.HIDDEN );
              }
          }.run( 500 );
      }
docs: Fade out the "Loading application" pop-up