add custom css to wordpress menu item

1function wpb_custom_new_menu() {
2  register_nav_menus(
3    array(
4      'my-custom-menu' => __( 'My Custom Menu' ),
5      'extra-menu' => __( 'Extra Menu' )
6    )
7  );
8}
9add_action( 'init', 'wpb_custom_new_menu' );
10

1<?php
2wp_nav_menu( array( 
3    'theme_location' => 'my-custom-menu', 
4    'container_class' => 'custom-menu-class' ) ); 
5?>
6

1// Wordpress apperance panel settings
21. Go to admin > appearance > menu
32. Click on Screen Options (top right of the screen)
43. Check the CSS classes options in the “Show advanced menu properties” panel
54. add your css classes to the element