TOPIC: Add CSS class/suffix to select fields?

Does anyone know of a way to add in an additional CSS class for specific fields?

I have a client that allows for members to receive a discount when registering. They have been getting complaints from a few members that they didn't receive their discount. I suspect a case of the members not being logged in, but the client is looking for a validation in the system.

I'd like to add a field that populates from the members Community Builder profile and just hide the field on the front-end with CSS. Is this possible, or does anyone have any suggestions for validating when someone is logged in when registering?

Please and Thanks.