i can not get second menu style

hello . i have mystique theme on my website

https://www.bilalfx.com

i used user function code to generate second menu as developer said in another topic , but even i get second menu , i could not get it styled. it shows menu items as horizontal list. How to get it styled , theme supported ? here the code that i used to generate second menu :

register_nav_menus(array('my_menu' => 'Top Header'));
add_action('mystique_header_start', 'my_menu');

function my_menu(){
  wp_nav_menu(array('container_class' => 'navigation', 'theme_location' => 'my_menu'));
}