Slidepress — How do I center a Slideshow Pro gallery on a page?

I would like my Slideshow Pro gallery on https://philipus.com/macro to be centered on the page, with white space margins on the rigth and left sides.

I have tried centering the slidepress tag, ie <p style="text-align: center;">[slidepress gallery='macro']</p> but that doesn’t work.

Any ideas how I can achieve this?

Thanks very much for your help.
/p