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

#-*- coding: utf-8 -*-
from kivy.config import Config
from kivy.uix.button import Button

Config.set('graphics', 'width', 300)
Config.set('graphics', 'height', 300)

from kivy.lang import Builder
Builder.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 App
from kivy.uix.widget import Widget
from kivy.uix.button import Button

from kivy.properties import StringProperty


class 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.count


class 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.

enter image description here

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

<MyOption@SpinnerOption>:
    font_size: 30

Spinner:
    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?