menus.php

<?php
namespace App;

/**
 * Set the Flexbox "order" of half the menu-items so that we can center the logo between them.
 */
add_action( 'wp_enqueue_scripts', function() {
  
  // Get menu object
  $theme_locations = get_nav_menu_locations();
  
  $menu = get_term( $theme_locations['primary_navigation'], 'nav_menu' ); 
  
  // Set up the CSS to return
  $custom_css = "
    .navbar-nav li:nth-of-type(n+" . floor(($menu->count/2) +2) . ") {
      order: 2;
    }
  ";
  
  // Register a style to add inline styles after
  wp_register_style( 'my-inline-style', false );
 
  // Enqueue the style
  wp_enqueue_style( 'my-inline-style' );
 
  // Add our inline styles
  wp_add_inline_style( 'my-inline-style', $custom_css );
} );