//add backend css
$myCssFileSrc = plugins_url( '/assets/css/style-backend.css', __FILE__ );
wp_enqueue_style( 'style-backend.css', $myCssFileSrc );
//add backend css
$myCssFileSrc = plugins_url( '/assets/css/style-backend.css', __FILE__ );
wp_enqueue_style( 'style-backend.css', $myCssFileSrc );