How to match the font size of Kivy Spinner's Label with the font size of the Values

I have created a UI using Python's Kivy with the following code.

#-*- coding: utf-8 -*-from kivy.config import Configfrom kivy.uix.button import ButtonConfig.set('graphics', 'width', 300)Config.set('graphics', 'height', 300)from kivy.lang import BuilderBuilder.load_string("""<AddItemWidget>:    BoxLayout:        size: root.size        orientation: 'vertical'        RecycleView:            size_hint: 1.0,1.0            BoxLayout:                id: box                size_hint_y: 1.0                orientation: 'vertical'                Spinner:                    id: root_spinner                    font_size: 8                    size_hint_y: 0.2                    text: 'test1'                    values: 'test1', 'test2', 'test3'                Label:                    size_hint_y: 0.8                    id: addButton                    text: "Test Label"""")from kivy.app import Appfrom kivy.uix.widget import Widgetfrom kivy.uix.button import Buttonfrom kivy.properties import StringPropertyclass AddItemWidget(Widget):    def __init__(self, **kwargs):        super(AddItemWidget, self).__init__(**kwargs)        self.count = 0    def buttonClicked(self):        self.count += 1        newButt = Button(text='Button'+ str(self.count),size_hint_y=1.0)        self.ids.box.add_widget(newButt, index=1)        self.ids.box.size_hint_y = 1.0 + 1.0 * self.countclass TestApp(App):    def __init__(self, **kwargs):        super(TestApp, self).__init__(**kwargs)    def build(self):        return AddItemWidget()if __name__ == '__main__':    TestApp().run()

When I specified the font size for a Spinner, I noticed that the font size displayed in the dropdown did not change.

By using SpinnerOption, I can change the font size in the dropdown.

<MyOption@SpinnerOption>:    font_size: 30Spinner:    id: root_spinner    font_size: 8    size_hint_y: 0.2    text: 'test1'    values: 'test1', 'test2', 'test3'    option_cls: "MyOption"

However, in this case, I need to specify the value within the scope of SpinnerOption. I tried something like this, but it didn't work.

<MyOption@SpinnerOption>:    font_size: self.font_size

I have also tried the following code, but it does not work.

<MyOption@SpinnerOption>:    font_size: AddItemWidget.root_spinner.font_size

How can I make the font size of the dropdown values match the font size of the root_spinner?