clock.kv

<Label>:
    font_name: 'Roboto'
    font_size: 60
    markup: True

<RobotoButton@Button>:
    background_normal: 'button_normal.png'
    background_down: 'button_down.png'
    border: (2, 2, 2, 2)
    font_name: 'Roboto'
    font_size: 25
    bold: True

BoxLayout:
    orientation: 'vertical'

    Label:
        id: time
        text: '[b]00[/b]:00:00'

    BoxLayout:
        height: 90
        orientation: 'horizontal'
        padding: 20
        spacing: 20
        size_hint: (1, None)

        RobotoButton:
            id: start_stop
            text: 'Start'
            on_press: app.start_stop()

        RobotoButton:
            id: reset
            text: 'Reset'
            background_normal: 'red_button_normal.png'
            background_down: 'red_button_down.png'
            on_press: app.reset()

    Label:
        id: stopwatch
        text: '00:00.[size=40]00[/size]'