main.py

from kivy.app import App
from kivy.uix.widget import Widget

class RootWidget(Widget):
    pass

class TestApp(App):

    def build(self):
        pass

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

test.kv

RootWidget:

<RootWidget>:
	FloatLayout:
		size: root.size
		pos: root.pos
		BoxLayout:
			text1: text1
		    orientation: "vertical"
		    size_hint_y: None
		    height: 120
		    padding: (0, (self.height - text1.texture_size[1]*4)/2)
		    canvas:
		    	Color:
		    		rgb: 1, 0, 0
		    	Rectangle:
		    		pos: self.pos
		    		size: self.size
		    Label:
		    	id: text1
		        text: '1'
		        halign: "left"
		        valign: "top"
		        size_hint: (None, None)
		        size: self.texture_size
		    Label:
		        text: '2'
		        halign: "left"
		        valign: "middle"
		        color: (0, 1, 0, 1)
		        size_hint: (None, None)
		        size: self.texture_size
		    Label:
		        halign: "left"
		        valign: "middle"
		        text: '3'
		        size_hint: (None, None)
		        size: self.texture_size
		    Label:
		        halign: "left"
		        valign: "bottom"
		        text: '4'
		        size_hint: (None, None)
		        size: self.texture_size