使用按钮的background_normal、background_down和border来实现此目的。让我们将您提供的两张图片命名为Norm.png和down.png。请参考下面的示例了解详细信息。

代码段

Button:
    background_normal: 'normal.png'
    background_down: 'down.png'
    border: 30,30,30,30

示例

main.py

import kivy
kivy.require('1.10.0')

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder

Builder.load_string("""
<RoundedButtons>:
    orientation: 'vertical'
    Button:
        text: '[color=3333ff][b]Rounded Button 1[/b][/color]'
        markup: True
        background_normal: 'normal.png'
        background_down: 'down.png'
        border: 30,30,30,30
    Button:
        text: '[color=ff3333][b]Rounded Button 2[/b][/color]'
        markup: True
        background_normal: 'normal.png'
        background_down: 'down.png'
        border: 30,30,30,30
""")


class RoundedButtons(BoxLayout):
    pass


class TestApp(App):
    def build(self):
        return RoundedButtons()


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

输出