Enqueue additional stylesheets for sites running Paid Memberships Pro

my_theme_pmpro_init_styles.php

<?php
/**
 * Integration for Paid Memberships Pro
 *
 * @package My_Theme_Name
 */

// Enqueue additional stylesheets for sites running Paid Memberships Pro
function my_theme_pmpro_init_styles() {
	if ( defined( 'PMPRO_VERSION' ) ) {
		wp_enqueue_style( 'paid-memberships-pro-customizations', get_template_directory_uri() . '/css/paid-memberships-pro.css', array(), '1.0' );
	}
}
add_action( 'wp_enqueue_scripts', 'my_theme_pmpro_init_styles' );