navmenu_template.kv

<NavMenu>:
    slide_button: slide_button
    menu_grid: menu_grid

    auto_bring_to_front: True
    size_hint_x: 0.2
    size_hint_y: 0.2
    pos: (-self.width + slide_button.width,0)

    orientation: 'horizontal'
    rows: 1

    BoxLayout:
        id: menu_grid
        orientation: 'vertical'

        MyCustomWidget1
        MyCustomWidget2


    Button:
        id: slide_button
        text: ">"
        width: self.texture_size[1]
        size_hint_x: None
        on_release: root.menu_open = not root.menu_open