can i give some background image in module load like this code
and how the code ?
Code:
public class Sisfo implements EntryPoint {
    private TextField<String> txtUser;
    private TextField<String> txtPwd;
    private Dialog login;
    private Viewport vp;
    
    public void onModuleLoad() {
        
         login=new Dialog(){
         @Override 
         protected void onButtonPressed(Button button){
             //super.onButtonPressed(button);
             if(button.getItemId()==Dialog.OK){
                 SecurityServiceAsync svc=GWT.create(SecurityService.class);
                 svc.ftr(txtUser.getValue(), txtPwd.getValue(), new AsyncCallback<List<String>>(){
                    @Override
                    public void onFailure(Throwable caught) {
                        // TODO Auto-generated method stub
                        MessageBox.alert("login", caught.getMessage(), null);
                    }
                    @Override
                    public void onSuccess(final List<String> ftrs) {
                        // TODO Auto-generated method stub
                        final MessageBox box = MessageBox.wait("Progress",  
                                "Now Loading, please wait...", "Login...");  
                            Timer t = new Timer() {  
                              @Override  
                              public void run() {  
                                  halaman(ftrs);  
                                box.close();  
                              }  
                            };  
                            t.schedule(3000);  
                     
                        
                        login.hide();
                    }                     
                 });
             }
                 
             }
         };
         login.setSize(330, 120);
         login.setHideOnButtonClick(false);
         //ToolBar tb=new ToolBar(); 
            //tb.add(new FillToolItem());  
            
            //tb.add(new SeparatorToolItem());
            //tb.add(selector); 
            
        login.setLayout(new FormLayout());
    login.setHeaderVisible(true);
    login.setHeading("Login Form");
    login.setSize(320, 200);
    
    HBoxLayoutData flexo = new HBoxLayoutData(new Margins(0, 5, 0, 0));  
    flexo.setFlex(1);  
    login.add(new Text(), flexo); 
        txtUser=new TextField<String>(); 
        txtUser.focus();
        txtUser.setFieldLabel("User Name"); 
        login.add(txtUser); 
        txtPwd=new TextField<String>();
        txtPwd.setPassword(true);
        txtPwd.setFieldLabel("Password");
        login.add(txtPwd); 
        
        HBoxLayoutData flex = new HBoxLayoutData(new Margins(0, 5, 0, 0));  
        flex.setFlex(1);  
        login.add(new Text(), flex);  
        ThemeSelector selector = new ThemeSelector(); 
        selector.setFieldLabel("Theme");
        login.add(selector);
        login.setClosable(false);
        login.setResizable(false);
        login.setButtons(Dialog.OK);
         
    //    login.setHideOnButtonClick(true);
        login.show();
        
         
        
    }
    
        public void halaman(List<String> ftrs){
            RootPanel rp=RootPanel.get("main");
        
            vp=new Viewport();
            rp.add(vp);

            
            Dispatcher d=Dispatcher.get();
            MainController mc=new MainController();
            d.addController(mc);
            
            
            vp.setLayout(new BorderLayout());
            
            BorderLayoutData northData = new BorderLayoutData(LayoutRegion.NORTH);
            ContainerData ac=new ContainerData(vp, northData);
            Dispatcher.get().dispatch(atasEvent.DISPLAY, ac);
            //northData.setSize(100);
            //northData.setMargins(new Margins(0, 0, 5, 0)); 
            vp.layout(true);
            
            
            BorderLayoutData westData = new BorderLayoutData(LayoutRegion.WEST);
            ContainerData dc=new ContainerData(vp, westData);
            FastMap<Object> map=new FastMap<Object>();
            map.put("ftrs", ftrs);
            dc.setData(map);
            westData.setSplit(true);
            westData.setSize(200);
            westData.setMaxSize(400);
            westData.setCollapsible(true);
            Dispatcher.get().dispatch(treeEvent.DISPLAY, dc);
    
            BorderLayoutData centerData = new BorderLayoutData(LayoutRegion.CENTER);
            ContainerData cd=new ContainerData(vp, centerData);
            Dispatcher.get().dispatch(menuEvent.DISPLAY, cd);
            vp.layout(true);
                    
        }
    
        
    
}