This is a great tutorial on how to create a resizable sticky bar. In case the site goes away here is the source file.
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
<?php wp_nav_menu( array( 'menu' => 'Menu Name', 'sort_column' => 'menu_order',
'container_class' => 'menu-header', 'theme_location' => 'primary', 'link_before' => '<span>',
'link_after' => '</span>' ) );
For custom menus replace “Menu Name” […]