Hide Background screen

Hi,

I am new to webdynpro abap.

I  created webdynpro application -portal development.

How to hide background screen when pop up message displayed and i want call initial screen when i click ok button in pop up window.

if lt_msg is not INITIAL.

lo_api_component = wd_comp_controller->wd_get_api( ).

     lo_window_manager = lo_api_component->get_window_manager( ).

     lo_window = lo_window_manager->create_popup_to_confirm(

                                        text                 = lt_msg

                                        button_kind          = if_wd_window=>co_buttons_ok

                                        message_type         = if_wd_window=>co_msg_type_error

                                        close_button         = abap_true

                                        default_button       = if_wd_window=>co_button_ok

                                        window_title         = 'Error List'

                                        window_width         = '35%'

                                        window_height        = '20%' ).

  lo_window->open( ).