from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from kivy.lang import Builder

Builder.load_string('''
<Demo>:
    orientation: 'vertical'
    BoxLayout:
        orientation: 'horizontal'
        height: self.minimum_height
        size_hint_y: None
        Button:
            size_hint_y: None
            height: 100
            pos_hint: {'center_y': 0.5}
            text: '1'
            y: 50
        Button:
            size_hint_y: None
            height: 200
            text: '2'
        Button:
            size_hint_y: None
            pos_hint: {'top': 1}
            height: 300
            text: '3'
        Button:
            size_hint_y: None
            height: 400
            text: '4'
    Button:
        text: 'Remaining space'
''')


class Demo(BoxLayout):
    pass


class DemoApp(App):
    def build(self):
        return Demo()


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