By default, the CellTable is surrounded with a border. To remove it, customize the generated gap class:
protected void configureObjectMetaDataById(int ID, Object object) { super.configureObjectMetaDataById(ID, object); switch (ID) { case LAYOUTMANAGER: LayoutManager locallayoutManager = (LayoutManager) object; //remove margin for cell table locallayoutManager.setMarginWidth(0); locallayoutManager.setMarginHeight(0); break; default: break; } }