'Return the sidebar_box, which contains all the elements of the
sidebar.'

def get_box(self):

    search_entry = self.create_search_entry()
    scrollable_view = self.scrollable_view()
    button_box = self.button_box()
    sidebar_box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
    sidebar_box.pack_start(search_entry, False, False, 0)
    sidebar_box.pack_start(scrollable_view, True, True, 0)
    sidebar_box.pack_start(button_box, False, True, 0)
    return sidebar_box
