Simple Payment enables you the use of a few pre-established forms

Legacy: Legacy form uses basic HTML & javascript, no additional frameworks, use for basic fields only.

Bootstrap Basic: Using Bootstrap 4 to validate fields and give it a bit more of style. (Your theme/website must have support to Bootstrap 4)

Bootstrap: as Bootstrap Basic, but shows additional fields to get client details, address etc.

Donation: A simple form for donation (using Bootstrap 4) with an open amount field so the user can type-in his donation.