如何不变地显示kivy按钮的背景图像？

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout

class MyApp(App):
    def build(self):
        layout = BoxLayout(orientation='vertical')
        
        # 创建按钮并设置背景图像
        button = Button(text='My Button', background_normal='path/to/your/image.png')
        layout.add_widget(button)
        
        return layout

if __name__ == '__main__':
    MyApp().run()