from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
Builder.load_string('''
<caja>:
    StackLayout:
        spacing: 5
        padding: 5
        orientation: 'tb-rl'
        Button:
            text: "boton1"
            size_hint: 0.15, 0.15
        Button:
            text: "boton2"
            size_hint: 0.25, 0.25
        Button:
            text: "boton3"
            size_hint: 0.35, 0.35
''')
class Caja(BoxLayout):
    pass

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

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