public static function append_deprecated_fields( $fields = array() ) {
		global $post;

		if ( class_exists( 'PUM_ATB' ) && has_action( 'popmake_popup_theme_overlay_meta_box_fields' ) ) {
			ob_start();

			do_action( 'popmake_popup_theme_overlay_meta_box_fields', $post->ID );

			$content = self::fix_deprecated_fields( ob_get_clean() );

			$fields['overlay']['background']['deprecated_fields'] = array(
				'type'     => 'html',
				'content'  => $content,
				'priority' => 999,
			);

			// Remove duplicate fields.
			unset( $fields['overlay']['background']['overlay_background_color'] );
			unset( $fields['overlay']['background']['overlay_background_opacity'] );
		}

		if ( class_exists( 'PUM_ATB' ) && has_action( 'popmake_popup_theme_container_meta_box_fields' ) ) {
			ob_start();

			do_action( 'popmake_popup_theme_container_meta_box_fields', $post->ID );

			$content = self::fix_deprecated_fields( ob_get_clean() );

			$fields['container']['background']['deprecated_fields'] = array(
				'type'     => 'html',
				'content'  => $content,
				'priority' => 999,
			);

			// Remove duplicate fields.
			unset( $fields['container']['background']['container_background_color'] );
			unset( $fields['container']['background']['container_background_opacity'] );
		}

		if ( class_exists( 'PUM_ATB' ) && has_action( 'popmake_popup_theme_close_meta_box_fields' ) ) {
			ob_start();

			do_action( 'popmake_popup_theme_close_meta_box_fields', $post->ID );

			$content = self::fix_deprecated_fields( ob_get_clean() );

			$fields['close']['background']['deprecated_fields'] = array(
				'type'     => 'html',
				'content'  => $content,
				'priority' => 999,
			);

			// Remove duplicate fields.
			unset( $fields['close']['background']['close_background_color'] );
			unset( $fields['close']['background']['close_background_opacity'] );
		}

		return $fields;
	}