class TestApp(App):
    def build(self):
        f1 = FloatLayout(size_hint=(None, None), size=(300, 300))
        f1.add_widget(Button(
            text="Кнопка",
            font_size=30,
            on_press=self.btn_press,
            size_hint=(0.5, 0.25),
            pos=(160, 0)
        ))
        return f1

 FlatLayout(size_hint=(None, None), width=300, height=200)

 from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.floatlayout import FloatLayout
from kivy.core.window import Window
class TestApp(App):
    def build(self):
        f1 = FloatLayout(size_hint=(None, None), size=(300, 300))
        button = Button(
            text="Кнопка",
            font_size=30,
            on_press=self.btn_press,
            size_hint=(0.5, 0.25),
            pos=(160, 0)
        )
        f1.add_widget(button)
        # Set window size to match layout size
        Window.size = f1.size
        return f1
    def btn_press(self, instance):
        pass  # Define your button press action here
if __name__ == '__main__':
    TestApp().run()