The layout of the donation form uses HTML tables to achieve the layout. Tables are no longer commonly used, and forces a two column layout of labels and input boxes. For a more responsive and better, more modern user experience that is more flexible in its' customization, I recommend that the HTML tables are removed and replaced with div's, label's, and CSS for formatting.
You can do a fair bit with the table/tbody/tr/td elements using CSS - changing their display to 'block' or using flex display can get a responsive layout without too much effort. This stops them from behaving like tables and you can treat them like regular DIV elements.
Completely agree. We just spent $4,000 to a consultant to restyle our forms to be somewhat responsive. If they were no longer table based, we could achieve better usability.