Custom CSS manipulation for donate_button on Fundraising Plugin

Dear Support,

I am struggling to centre align a "donate_button" shortcode. All attempts leave it left aligned. Whether I try through the Custom CSS in the Fundraising settings or whether I try and centre within the text box the shortcode is sitting in.

I have also tried different styling (basic, minimal, etc) but to no avail.

I am focusing my attention on form.wdf-basic/form.wdf-minimal in the Custom CSS. Perhaps I am looking/trying in the wrong place?

I have attached an image for clarity. The site is currently in development at the donate buttons are on the home page.

Thanks in advance to anyone out there who can point me in the right direction.

All good wishes,