Hi there - the Shop Pay dynamic checkout button is generated using the `payment_button` Liquid filter, rather than being created in the code of the theme, so it's different to regular buttons where you'd typically be able to assign specific class name or ID to the `<button>` element.
Because this is an element that is generated by Shopify, it's not recommended that you alter it's appearance as this could result in unintended consequences, for example breaking the payment form functionality or performance issues.
Hope this helps!
