I would like to override some mark-up and css (like <div class="soma_container"><ul class=""></ul></div>)styling on a chosen custom menu widget. How would I do that? Should be hooked as the main navigation in functions.php or if there is good tutorial on this would be really appreciated

I would like to override some mark-up and css (like <div class="soma_container"><ul class=""></ul></div>)styling on a chosen custom menu widget. How would I do that? Should be hooked as the main navigation in functions.php or if there is good tutorial on this would be really appreciated

I think a some of the thing I can make on widget poition init

  register_sidebar(array(
    'name'          => __('Sidebar Menu', 'roots'),
    'id'            => 'sidebar-primary',
    'before_widget' => '<section class="widget %1$s %2$s">',
    'after_widget'  => '</section>',
    'before_title'  => '<h3>',
    'after_title'   => '</h3>',
  ));

but how would override the list css for the custom menu