Register new admin scripts

Hi! I am try to add some js and css scripts to a custom field, but I am lost, any idea?
Regars!

function initialize() {
add_action( 'siteorigin_widgets_before_widget_select-news', array( $this->id_base, 'enqueue_widget_scripts' ),10,2 );}

function enqueue_widget_scripts($instance, $widget){
    wp_enqueue_style('select2', '//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css', [], null);
    wp_enqueue_script('select21', 'https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js', [], null, true);}