The Registration Form may take on the look of a theme and may not match with how you want it to appear. It may pull elements from the theme styling (boxes around the fields, etc.)
In a case like this, the Registration Form Style can be adjusted in the Advanced Options > Registrations > Registration Settings section in WishList Member.
The option to set the Registration Form Style to “WishList Member Styled” can be used.
This should result in the registration form taking on a more uniform appearance.