private function add_main_field( $config_id, $args ) {

		/**
		 * Add a hidden field, the label & description.
		 */
		Kirki::add_field(
			$config_id,
			wp_parse_args(
				[
					'type'              => 'kirki-generic',
					'sanitize_callback' => isset( $args['sanitize_callback'] ) ? $args['sanitize_callback'] : [ __CLASS__, 'sanitize' ],
					'choices'           => [
						'type'        => 'hidden',
						'parent_type' => 'kirki-typography',
					],
				],
				$args
			)
		);
	}