Subnav-line centered menu

Hi I am wanting to use subnav-line in the small footer menu at https://www.applifting.cf

which is already centered, but when I add the class in wp_nav_menu (ive used the standard WP function), it throws it off to the left, I have tried a variety of ways to center it with no joy?

here is code which puts it there

function slift_register_nav_menu(){ register_nav_menus( array( 'footer_menu' => __( 'Footer Menu', 'sectionlift' ), ) ); } add_action( 'after_setup_theme', 'slift_register_nav_menu', 0 );

and in the footer html is

// Display the footer & social widget area in the front end. add_action( 'beans_footer_before_markup', 'footer_widget_area' ); function footer_widget_area() { // Stop here if no widget if( !beans_is_active_widget_area( 'footer' ) ) return; ?>

              'Footer Menu',
            )); ?>

 'uk-subnav uk-subnav-line'

Any tips welcome

thanks