Fin.kv

#:import FadeTransition kivy.uix.screenmanager.FadeTransition
MDScreen:
    name: 'Export'
    MDNavigationLayout:

        ScreenManager:

            MDScreen:

                MDBoxLayout:
                    orientation: "vertical"

                    MDBoxLayout:

                        MDNavigationRail:
                            id: navigation_rail
                            md_bg_color: "#377BFF"
                            selected_color_background: "#19F498"
                            ripple_color_item: "#19F498"
                            on_item_release: app.switch_screen(*args)
                            padding: 24

                            MDNavigationRailMenuButton:
                                icon:'arrow-left'
                                text: 'Retour'
                                on_press:
                                    root.manager.transition.direction = "right"
                                    root.manager.current = "centre"

                            MDNavigationRailItem:
                                text: "Python"
                                icon: "language-python"

                            MDNavigationRailItem:
                                text: "JavaScript"
                                icon: "language-javascript"

                            MDNavigationRailItem:
                                text: "CPP"
                                icon: "language-cpp"

                            MDNavigationRailItem:
                                text: "Swift"
                                icon: "language-swift"

                        ScreenManager:
                            id: screen_manager
                            transition:
                                FadeTransition(duration=.2, clearcolor=app.theme_cls.bg_dark)