While you were making your test payments you probably noticed that several of the pages on your site looked a little plain. You'll probably want to style these files with whatever CSS and markup you want:
- index.php - the donation form
- success.php - where users are redirected after successful payments
- cancelled.php - where users are sent after cancelling a payment
- paypal_submit.php - a temporary page that appears after the user submits the form. The user is automatically redirected from this page to PayPal.