You can choose the colours, fonts, and style for the inputs & buttons used by your forms - to do this go to Forms | Branding and click on the Form Appearance tab.
As shown in the example below as you change the form appearance the preview will update to show how your form will look - when you are happy with the appearance press the Save Changes button.
The form appearance you have set up will then be used for all your forms when they are displayed.
The Donorfy Academy features a learning course for Donation Forms - enrol here