Kivy adding background color and button to change screen

I'm trying to make a simple app with kivy but I'm stuck with some tasks, I want to change the background in a light blue color and I want a button under my title that says "Begin opiniepeiling". I can't find any code online that works for me and I wouldn't know how to integrate it into my code. Does some of you guys have some tips and tricks for me to help me get further? This is the (simple) code I have so far.

from kivy.app import App from kivy.uix.label import Label

class MainApp(App):
    def build(self):
        label = Label(text='Meedia Dagbesteding Client & Begeleider',
                      font_size='40sp',
                      size_hint=(.5, .5),
                      pos_hint={'center_x': .5, 'center_y': .5},
                      font_name="Arial",)

        return label

if __name__ == '__main__':
    app = MainApp()
    app.run()

This code writes a simple window with some text in the middle with a nice font, this is the very beginning. I had some more code that would give me another screen but only after closing this window and that is not what I need. I want to be able to create a new window or change my window into something else.

I hope this doesn't feel like asking others to do it for me. I'm stuck and could use some tips and tricks to help me get further.

Thanks all!