If you want to add an html element such as a span or strong tag to your native WordPress menu in or navigation here is a snippet for that. The following code replaces or modifies your existing code that links to your menu
'Menu Name', 'sort_column' => 'menu_order',
'container_class' => 'menu-header', 'theme_location' => 'primary', 'link_before' => '',
'link_after' => '' ) );
?>
For custom menus replace “Menu Name” with the name of your menu. If you just have a default WordPress menu. The “link_before” and “link_after” areas will place the element(s) before and after your Menu link.