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;
}
}