Thank you, @lat9, for this latest version.

Although the checkout_one_confirmation page is transitory (given the payment methods I use) it can still v.briefly display and as such I would like to style it to match the rest of the pages on my custom template site. Would there be a way to hold that page so that I can more easily apply changes to my tpl_checkout_one_confirmation_default.php and css, before it proceeds to the checkout_success page?

The obvious way would be to setup a payment method that uses this page - one that takes c.cards on site - but I'm not sure how far down that path I would need to go, so ideally I would like to temporarily break something so that it doesn't progress past that page.