from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.textinput import TextInput
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition
from kivy.uix.widget import Widget
from kivy.lang import Builder

class LoginScreen(GridLayout):
    def __init__(self, **kwargs):
        super(LoginScreen, self).__init__(**kwargs)
        self.cols = 2
        self.add_widget(Label(text="Username:"))
        self.username = TextInput(multiline=False)
        self.add_widget(self.username)

        self.add_widget(Label(text="Password:"))
        self.password = TextInput(multiline=False, password=True)
        self.add_widget(self.password)

        self.add_widget(Label(text="Two Factor Auth:"))
        self.tfa = TextInput(multiline=False)
        self.add_widget(self.tfa)

class MainScreen(Screen):
    pass

class AnotherScreen(Screen):
    pass

class ScreenManagement(ScreenManager):
    pass

presentation = Builder.load_file("screen.kv")

class SimpleKivy(App):
    def build(self):
        return presentation

if __name__ == "__main__":
    SimpleKivy().run()

#: import FadeTransition kivy.uix.screenmanager.FadeTransition

ScreenManagement:
    transition: FadeTransition()
    MainScreen:
    AnotherScreen:

<MainScreen>:
    name: "main"
    Button:
        color: 0,1,0,1
        font_size: 25
        size_hint: 0.3,0.2
        text: "Click"
        on_release: app.root.current = "other"
        pos_hint: {"right":1, "top":1}


<AnotherScreen>:
    name: "other"

    GridLayout:
        LoginScreen