How to: Add right aligned search box to main navigation

I know how to generally add a search box to the main menu (used code added):

add_filter(‘wp_nav_menu_items’,’add_search_box_to_nav_menu’, 10, 2);
function add_search_box_to_nav_menu( $items, $args ) {
if( $args->theme_location == ‘primary’ )
return $items.get_search_form();

return $items;
}
`
But I’m not able to modify the style.css, so that the box is aligned left.
Could anyone please help me?

Many thanks 🙂

sonix