an example of customizing keyboard widget in multi mode in kivy

multi.py

from kivy.config import Config
Config.set('kivy', 'keyboard_mode', 'systemandmulti')
from kivy.app import App
from kivy.lang import Builder
from kivy.factory import Factory
from kivy.animation import Animation as A
from kivy import properties as P


KV = '''
<KeyboardTextInput>:
    size_hint_y: None
    height: self.minimum_height
    target_pos: self.center_x, self.y
    multiline: False

GridLayout:
    cols: 2
    padding: 100
    spacing: 20
    KeyboardTextInput:
    KeyboardTextInput:
    KeyboardTextInput:
    KeyboardTextInput:
'''

class KeyboardTextInput(Factory.TextInput):
    target_pos = P.ListProperty([0, 0])

    def on_keyboard(self, *args, **kwargs):
        # super().on_keyboard(*args, **kwargs)
        if self.keyboard and self.keyboard.widget:
            w = self.keyboard.widget
            # w.layout = 'custom-keyboard.json'
            w.do_scale = False
            w.do_rotation = False

            if w.scale == 1:
                w.center_x = app.root.center_x
                w.scale = .5
                w.top = app.root.y

            w.opacity = 0
            w.center_x = self.target_pos[0]
            w.top = self.target_pos[1] - 20
            A(
                opacity=1,
                center_x=self.target_pos[0],
                top=self.target_pos[1],
                scale=1.2,
                t='out_sine',
                d=.5
            ).start(w)



class Application(App):
    def build(self):
        return Builder.load_string(KV)


if __name__ == "__main__":
    app = Application()
    app.run()