gtk对话框

Question

请问如何自定义对话框?例如我想定制一个带标签和两个按钮的对话框，提示用户是否关闭系统，确定和取消？该如何操作?我的代码如下：
GtkWidget *dialog = gtk_dialog_new();
label = gtk_label_new(NULL);      
gtk_dialog_set_has_separator(GTK_DIALOG(dialog), true);
gtk_label_set_markup(GTK_LABEL(label),"close system?");
gtk_box_pack_start_defaults(GTK_BOX(GTK_DIALOG(dialog)->vbox), label);

button=gtk_button_new_with_label("YES");
gtk_box_pack_start(GTK_BOX(GTK_DIALOG(dialog)->action_area),button,TRUE,TRUE,0);
gtk_signal_connect(GTK_OBJECT(button),"clicked",G_CALLBACK(gtk_main_quit),NULL);
gtk_widget_show(button);
               
button=gtk_button_new_with_label("NO");
gtk_box_pack_start(GTK_BOX(GTK_DIALOG(dialog)->action_area),button,TRUE,TRUE,0);
gtk_signal_connect(GTK_OBJECT(button),"clicked",G_CALLBACK(destroy),dialog);
gtk_widget_show(button);
gtk_widget_show(dialog);

这是我点击关闭按钮后的回调函数，提示用户是否真的关闭？可是标签内容不显示，对话框只显示分割线和两个按钮。。。请问各位大侠怎么回事？谢谢