Example of how to add the 'qbutton' class to the Stripe checkout 'pay now' button.

example.php

<?php //Please do not include the opening PHP tag if you already have one

function tw_ee_stripe_checkout_button_class() {
	
	wp_add_inline_script( 
		'espresso_stripe_payment_js',
		'jQuery( document ).ready(function($) {
			$("#ee-stripe-button-btn").addClass("qbutton");
		});'
	);
}
add_action( 'wp_enqueue_scripts', 'tw_ee_stripe_checkout_button_class', 11 );