Bootstrap 4 WP Navwalker多级下拉菜单

如何解决Bootstrap 4 WP Navwalker多级下拉菜单

基本上，我正在尝试将WP Navwalker下拉菜单设置为三个级别，而不是默认级别2。

我已经找到了相关的教程，但是它们似乎是Bootstrap 3的教程，因为我没有 .dropdown-submenu类。

这是我要执行的操作的示例，但这对我不起作用（我猜测是因为我没有 .dropdown-submenu 类）>

https://joeybabcock.me/blog/html/bootstrap-multi-level-dropdown-menus-in-wordpress/

<div class="container header_primary py-4 fw-c">
    <div class="row">
        <div class="col-lg-3 col-md-4 col-sm-6 col-6 d-flex align-items-center">
            <a href="<?PHP bloginfo('url'); ?>"><img src="<?PHP echo get_template_directory_uri(); ?>/images/logo-black.png" alt=""></a>
        </div><!-- .site-branding -->

        <div class="col-lg-8 col-md-8 col-sm-6 col-6 header_navigation justify-content-end align-items-center">
            <nav class="primary_style navbar navbar-expand-lg navbar-expand-md navbar-light float-md-right d-md-flex d-block">
                <button class="navbar-toggler float-right" type="button" data-toggle="collapse" data-target="#bs4navbar1" aria-controls="mobileNav" aria-expanded="false" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
                 <?PHP
                 wp_nav_menu([
                     'menu'            => 'main-nav','theme_location'  => 'top','container'       => 'div','container_id'    => 'bs4navbar','container_class' => 'collapse navbar-collapse','menu_id'         => false,'menu_class'      => 'navbar-nav','depth'           => 3,'fallback_cb'     => 'bs4navwalker::fallback','walker'          => new bs4navwalker()
                 ]);
                 ?>
            </nav>
        </div>
    </div>