Extra Menu

I’m adding an extra menu only on certain pages. I found this code in the codex:

wp_nav_menu( array( ‘theme_location’ => ‘extra-menu’, ‘container_class’ => ‘my_extra_menu_class’ ) );

The phase ‘container_class’ is just a wp term and the class I make up for it is my_extra_menu_class’, right? So when I style it in the css, I use

.my_extra_menu_class {}