Python | Set Background Template in kivy

# Program to create a background template for the App

# import necessary modules from kivy
from kivy.uix.boxlayout import BoxLayout
from kivy.app import App

# create a background class which inherits the boxlayout class
class Background(BoxLayout):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
    pass

# Create App class with name of your app
class SampleApp(App):

# return the Window having the background template.
    def build(self):
        return Background()

# run app in the main function
if __name__ == '__main__':
    SampleApp().run()

<Background>:
    id: main_win
    orientation: "vertical"
    spacing: 10
    space_x: self.size[0]/3


    canvas.before:
        Color:
            rgba: (1, 1, 1, 1)
        Rectangle:
            source:'back.jfif'
            size: root.width, root.height
            pos: self.pos
    Button:
        text: "Click Me"
        pos_hint :{'center_x':0.2, 'center_y':0.2}
        size_hint: .30, 0
        background_color: (0.06, .36, .4, .675)
        font_size: 40