diff --git a/hello_world.cpp b/hello_world.cpp
index 804d80d..87dbeb3 100644
--- a/hello_world.cpp
+++ b/hello_world.cpp
@@ -1,8 +1,7 @@
 #include "hello_world.hpp"
-#include <gtkmm/box.h>
+#include <gtkmm/listbox.h>
 
 namespace learn_gtkmm4 {
     HelloWorld::HelloWorld(BaseObjectType *cobject, const Glib::RefPtr<Gtk::Builder> &builder) :
-            Gtk::ApplicationWindow(cobject), m_builder(builder) {
-    }
+            Gtk::ApplicationWindow(cobject), m_builder(builder) {}
 } // learn_gtkmm4
\ No newline at end of file
diff --git a/hello_world.hpp b/hello_world.hpp
index 771a7d0..f3ab9a8 100644
--- a/hello_world.hpp
+++ b/hello_world.hpp
@@ -1,12 +1,10 @@
 #ifndef LEARNGTK4_HELLO_WORLD_HPP
 #define LEARNGTK4_HELLO_WORLD_HPP
 
+#include <glibmm/refptr.h>
 #include <gtkmm/applicationwindow.h>
 #include <gtkmm/builder.h>
 
-namespace Gtk {
-    class Box;
-}
 
 namespace learn_gtkmm4 {
 
@@ -20,7 +18,6 @@ namespace learn_gtkmm4 {
 
     protected:
         Glib::RefPtr<Gtk::Builder> m_builder;
-        Gtk::Box *m_ui_box{ nullptr };
     };
 
 } // learn_gtkmm4