How to use the voila.paths.ROOT function in voila

parent=self,
            connection_dir=self.connection_dir,
            kernel_spec_manager=self.kernel_spec_manager,
            allowed_message_types=[
                'comm_open',
                'comm_close',
                'comm_msg',
                'comm_info_request',
                'kernel_info_request',
                'shutdown_request'
            ]
        )

        jenv_opt = {"autoescape": True}  # we might want extra options via cmd line like notebook server
        env = jinja2.Environment(loader=jinja2.FileSystemLoader(self.template_paths), extensions=['jinja2.ext.i18n'], **jenv_opt)
        nbui = gettext.translation('nbui', localedir=os.path.join(ROOT, 'i18n'), fallback=True)
        env.install_gettext_translations(nbui, newstyle=False)
        self.contents_manager = LargeFileManager(parent=self)

        # we create a config manager that load both the serverconfig and nbconfig (classical notebook)
        read_config_path = [os.path.join(p, 'serverconfig') for p in jupyter_config_path()]
        read_config_path += [os.path.join(p, 'nbconfig') for p in jupyter_config_path()]
        self.config_manager = ConfigManager(parent=self, read_config_path=read_config_path)

        # default server_url to base_url
        self.server_url = self.server_url or self.base_url

        self.app = tornado.web.Application(
            base_url=self.base_url,
            server_url=self.server_url or self.base_url,
            kernel_manager=self.kernel_manager,
            kernel_spec_manager=self.kernel_spec_manager,

self.callback = tornado.ioloop.PeriodicCallback(lambda: self.ping(''), 6000)
        path = path.strip('/') + '.ipynb'
        if path not in event_handlers:
            handlers = []
            watchdog_observer = watchdog.observers.Observer()
            # sometimes useful to add this when triggering does not work
            from watchdog.events import LoggingEventHandler
            logging_handler = LoggingEventHandler()
            watchdog_observer.schedule(logging_handler, '.', recursive=True)

            notebook_handler = WatchDogEventHandler(regexes=['\\./' + path])
            watchdog_observer.schedule(notebook_handler, '.', recursive=True)
            handlers.append(notebook_handler)
            
            misc_handler = WatchDogEventHandler(regexes=[str(ROOT) +r'/templates/.*', str(ROOT / 'static/main.js'), str(ROOT / 'static/dist/libwidgets.js')])
            watchdog_observer.schedule(misc_handler, str(ROOT), recursive=True)
            handlers.append(misc_handler)
            
            watchdog_observer.start()
            event_handlers[path] = handlers
            
            tornado.autoreload.add_reload_hook(self._on_reload)

        self.handlers = event_handlers[path]
        for handler in self.handlers:
            handler.listeners.append(self)

template_paths = []

    # common configuration options between the server extension and the application
    voila_configuration = VoilaConfiguration(parent=server_app)
    collect_template_paths(
        nbconvert_template_paths,
        static_paths,
        template_paths,
        voila_configuration.template
    )

    jenv_opt = {"autoescape": True}
    env = Environment(loader=FileSystemLoader(template_paths), extensions=['jinja2.ext.i18n'], **jenv_opt)
    web_app.settings['voila_jinja2_env'] = env

    nbui = gettext.translation('nbui', localedir=os.path.join(ROOT, 'i18n'), fallback=True)
    env.install_gettext_translations(nbui, newstyle=False)

    host_pattern = '.*$'
    base_url = url_path_join(web_app.settings['base_url'])

    tree_handler_conf = {
        'voila_configuration': voila_configuration
    }
    web_app.add_handlers(host_pattern, [
        (url_path_join(base_url, '/voila/render/(.*)'), VoilaHandler, {
            'config': server_app.config,
            'nbconvert_template_paths': nbconvert_template_paths,
            'voila_configuration': voila_configuration
        }),
        (url_path_join(base_url, '/voila'), VoilaTreeHandler, tree_handler_conf),
        (url_path_join(base_url, '/voila/tree' + path_regex), VoilaTreeHandler, tree_handler_conf),