Custom CSS Classes on Fields Add-On easily extends the functionality of Profile Builder by allowing you to add custom CSS classes for fields.
This add-on is included in the main Profile Builder plugin. To activate the Custom CSS Classes on Fields Add-on navigate to the Add-ons page, locate it under the Free Add-ons sections and click Activate.
After you activate the add-on a new option will be available for your fields in Profile Builder → Form Fields.
The following field types will have a “CSS Class” text input in which you can add your own CSS classes for that field.