Хочу изменить местоположение этого текста, но когда меняю halign: "center" на halign: "top" программа завершает работу с ошибкой.

Вот код:
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivymd.app import MDApp
from kivymd.uix.boxlayout import MDBoxLayout
KV = '''
<ContentNavigationDrawer>
    ScrollView:
        MDList:
            OneLineListItem:
                text: "One"
                on_press:
                    root.nav_drawer.set_state("close")
                    root.screen_manager.current = "la 1"
            OneLineListItem:
                text: "Two"
                on_press:
                    root.nav_drawer.set_state("close")
                    root.screen_manager.current = "la 2"
                    
            OneLineListItem:
                text: "Three"
                on_press:
                    root.nav_drawer.set_state("close")
                    root.screen_manager.current = "la 3"
MDScreen:
    MDToolbar:
        id: toolbar
        pos_hint: {"top": 1}
        elevation: 10
        title: "MDNavigationDrawer"
        left_action_items: [["menu", lambda x: nav_drawer.set_state("open")]]
    MDNavigationLayout:
        x: toolbar.height
        ScreenManager:
            id: screen_manager
            MDScreen:
                name: "la 1"
                MDLabel:
                    text: "Screen 1"
                    halign: "center"
            MDScreen:
                name: "la 2"
                MDLabel:
                    text: "Screen 2"
                    halign: "center"
                    
            MDScreen:
                name: "la 3"
                MDLabel:
                    text: "Screen 3"
                    halign: "center"
        MDNavigationDrawer:
            id: nav_drawer
            ContentNavigationDrawer:
                screen_manager: screen_manager
                nav_drawer: nav_drawer
'''
class ContentNavigationDrawer(MDBoxLayout):
    screen_manager = ObjectProperty()
    nav_drawer = ObjectProperty()
class TestNavigationDrawer(MDApp):
    def build(self):
        return Builder.load_string(KV)
TestNavigationDrawer().run()