Could use Button styling and more styling options on Checkout Order Thank You template.
If someone views the page after the oders is marked as pending payment it will show pay & cancel buttons. (These have no magin between them) If it is downloadable product and the order is marked complete, a download button will show. No way to style those without custom CSS.
However, myself, I have already made custom CSS to style it.
It is lacking compared to other templates that show order. It took a load of custom CSS to fix it and make it look usable and responsive.
Actually, I think the no button margin is a bug rather than a feature request. 