You must have an HTML 5 Page Wrapper available for the donation form in order for the form to to be responsive and resize for mobile devices.

For more information on changing the Document Type Declaration on a Page Wrapper, please refer to this help documentation:  Change the document declaration type

Here are some additional tags you can use to optimize how the form displays on mobile devices:
  1. In the Additional HTML Tags for HEAD element section of the Page Wrapper, add this meta tag to control the width scaling:
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0;">
  1. On the Body Tag Attributes page, insert the following mobile class in the BODY tags:

Note: This content solution was provided by a web developer. Support cannot assist with the implementation or further troubleshooting of this custom code. Further assistance is available in the Blackbaud Community.