No CSS needed - you (if you are a Super Admin) can uncheck the priority options that you don’t want to use on your platform.  Admin > Advanced Settings > Enrollment Attributes > Priority - uncheck the ones you do not want to use. 

We did the same thing when we enabled the enrollment options - we kept “Required” since that’s the terminology that we use internally and also kept “Recommended” and disabled the other two options so our users don’t get confused by the similar options.

I did notice, however, if you already had enabled the option, they may appear greyed out and you can’t uncheck them.  I am assuming that is because they have already been used in some enrollments. If that’s the case, you may be able to track down any enrollments using those and change them to the ones you want to keep and then you may be able to turn the unwanted ones off.