gp-multi-page-navigation-add-current-class-custom-page-links.php

<?php
/**
 * Gravity Perks // Multi-page Navigation // Add "current" Class to Custom Page Links
 * https://gravitywiz.com/documentation/gravity-forms-multi-page-navigation/#custom-page-links
 */
add_action( 'wp_footer', function() {
	?>

	<script>
		( function( $ ) {
			$( document ).on( 'gform_post_render', function( e, formId, currentPage ) {
				$( '.gpmpn-page-link' ).removeClass( 'current' ).each( function() {
					var linkPage = $( this ).attr( 'href' ).split( '#' )[1];
					if( linkPage == currentPage ) {
						$( this ).addClass( 'current' );
					}
				} );
			} );
		} )( jQuery );
	</script>

	<?php
} );