for Article! Navbar B-4

header.php

<nav class="navbar navbar-expand-md navbar-dark bg-dark">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarDropdown" aria-controls="navbarDropdown" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>	
<a class="navbar-brand" href="<?php echo esc_url( home_url('/') ); ?>"><?php bloginfo('name'); ?></a>
    <div class="collapse navbar-collapse" id="navbarDropdown">
      <?php
        wp_nav_menu( array(
          'theme_location'  => 'navbar',
          'container'       => false,
          'menu_class'      => '',
          'fallback_cb'     => '__return_false',
          'items_wrap'      => '<ul id="%1$s" class="navbar-nav mr-auto mt-2 mt-lg-0 %2$s">%3$s</ul>',
          'depth'           => 2,
          'walker'          => new bootstrap_4_walker_nav_menu()
        ) );
      ?>
		<?php get_template_part('searchform'); ?>
    </div>
</nav>