content width of checkout/order-received page

Hello,
I was wondering if you know how to make the content of the checkout page/order-received smaller. I know how to make the content width of regular pages smaller ( .page-id-78 #content{max-width:800px;} )
but I only need this for the order-received part of the checkout page, not the regular checkout page where shipping, billing etc is shown, only on the endpoint order-received. Is this possible?