How to format 'Product Review' text box font ?

[akm]

Installed XThreads and all seems to be working fine.
Am very much a diy beginner (not a developer) with forum software, php, css, etc.
Trying to create a simple MyBB (with XThread plug-in) 'Product Review' forum.
Have been trying to find info for how to edit format (font-size, etc) of the (xthread) custom textboxes ?
Attached only file where could find with 'key' name used in the PR sub-forum.
But could not figure out how to find .css file or what ever file needed to edit the textbox font size.
Tried some ACP editing at 'Custom Thread Fields', but nothing seemed to work.
Also, havent done as much searching yet, but wondering how to delete (or edit to include) the MyBB 'Your Message:' text box from list of custom (xthread) text boxes.
Please let me know, if possible, where to find info on the above question/s, and let me know if need additional question info.
Thanks very much for your help.