Call to undefined method Template::append_css()

Call to undefined method Template::append_css()

I am trying to append_css using the code below. On older projects the
below code would normally work. For reference i am using CodeIgniter and
template Sparks
public function __construct() {
parent::__construct();
$this->load->library('template');
$this->template
->append_css('/public/css/app.css');
}
public function index(){
$this->template->build('welcome_message.php');
}
}
I get the following error
Fatal error: Call to undefined method Template::append_css() in
/Users/Afont/quals/codeigniter-test/application/controllers/welcome.php on
line 9