The documentation says
"For the advanced designers, there is also a field for Custom CSS.
This field can be used to input raw CSS that corresponds to the
HTML in our hosted payment pages."
But I can't find anywhere the documentation for the CSS fields.
So I went ahead and looked at the page and found the variables that
are used in the page like
.container and .contentBox. I'm able to customize the page to look
the way I want it to, but want to make sure that these variables
are not going to change in future versions.

#1 Posted by Marc Guyer Support staff on 16 Dec, 2011 09:49 PM
If we make any changes, we will make sure they don't affect custom css. If any markup changes will affect custom css, we will version the markup to maintain backward compatibility.
Dean closed this discussion on 18 Jan, 2013 03:56 PM.