test.py

from kivy.app import App
from kivy.metrics import dp
from kivy.uix.behaviors import TouchRippleBehavior
from kivy.uix.button import Button
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout


KV = """
<RectangleFlatButton>:
    ripple_color: 0, 0, 0, .2
    background_color: 0, 0, 0, 0
    color: root.primary_color

    canvas.before:
        Color:
            rgba: root.primary_color
        Line:
            width: 1
            rectangle: (self.x, self.y, self.width, self.height)

Screen:
    canvas:
        Color:
            rgba: 0.9764705882352941, 0.9764705882352941, 0.9764705882352941, 1
        Rectangle:
            pos: self.pos
            size: self.size
"""


class RectangleFlatButton(TouchRippleBehavior, Button):
    primary_color = [
        0.12941176470588237,
        0.5882352941176471,
        0.9529411764705882,
        1
    ]

    def on_touch_down(self, touch):
        collide_point = self.collide_point(touch.x, touch.y)
        if collide_point:
            touch.grab(self)
            self.ripple_show(touch)
            return True
        return False

    def on_touch_up(self, touch):
        if touch.grab_current is self:
            touch.ungrab(self)
            self.ripple_fade()
            return True
        return False

def get_hor_boxlayout(orientation='horizontal', padding=10, spacing=10):
    return BoxLayout(orientation=orientation, padding=padding, spacing=spacing)

class MainApp(App):
    def build(self):
        screen = Builder.load_string(KV)
        hor = get_hor_boxlayout()
        hor.add_widget(RectangleFlatButton(
                text="Hello, World",
                pos_hint={"center_x": 0.5, "center_y": 0.5},
                size_hint=(None, None),
                size=(dp(110), dp(35)),
                ripple_color=(0.8, 0.8, 0.8, 0.5),
            ))
        hor.add_widget(RectangleFlatButton(
            text="Hello, World",
            pos_hint={"center_x": 0.5, "center_y": 0.5},
            size_hint=(None, None),
            size=(dp(110), dp(35)),
            ripple_color=(0.8, 0.8, 0.8, 0.5),
        ))
        screen.add_widget(hor)

        return screen


MainApp().run()