function projekt_todo_custom_menu_class()
{

	global $menu;

	foreach ( $menu as $key => $value ) {
		if ( 'Projekt-ToDos' == $value[0] ) {
			$menu[ $key ][4] .= " projekt_todo_custom_menu_class";
		}
	}
}

add_action( 'admin_init', 'projekt_todo_custom_menu_class' );