code: public void showPageOverlay() {
  
          if (m_overlay == null) {
              m_overlay = new SimplePanel();
              m_overlay.setStyleName(I_CmsLayoutBundle.INSTANCE.dialogCss().popupOverlay());
              Style style = m_overlay.getElement().getStyle();
              style.setWidth(100, Unit.PCT);
              style.setHeight(100, Unit.PCT);
              style.setPosition(Position.FIXED);
          }
          RootPanel.get().add(m_overlay);
      }
docs: Shows a page overlay preventing user actions.<p>