mypmpro-element-class-sydney.php

<?php
/**
 * This recipe will add in the necessary classes to PMPro Buttons, ensuring they
 * have the same look & feel as your theme: Sydney
 *
 * https://wordpress.org/themes/sydney/
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function mypmpro_sydney_classes( $class, $element ){

	if ( in_array( 'pmpro_btn', $class ) ) {
		$class = array();
		$class[] = 'roll-button';
	}

	return $class;

}
add_action( 'pmpro_element_class', 'mypmpro_sydney_classes', 10, 2 );

This recipe is included in the post on "Using the Sydney Theme by aThemes with Paid Memberships Pro" at Paid Memberships Pro here: https://www.paidmembershipspro.com/sydney-theme-by-athemes-paid-memberships-pro/