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IN FUNCTIONS.PHP
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/**
 * Add class to menu-1 to active menu link.
 */
 
add_filter( 'nav_menu_css_class', 'special_nav_class', 10, 3 );
function special_nav_class( $classes, $item, $args ) {
    if ( 'menu-1' === $args->theme_location ) {
        if (in_array('current-menu-item', $classes) ){
            $classes[] = 'main-nav__link_active ';
        }
    }

    return $classes;
}