apply_filters( 'nav_menu_css_class', string[] $classes, WP_Post $menu_item, stdClass $args, int $depth )

Parameters

$classes

Array of the CSS classes that are applied to the menu item's <li> element.

$menu_item

The current menu item object.

$args

An object of wp_nav_menu() arguments.

$depth

Depth of menu item. Used for padding.