Centering text and images on Nook

My CSS for centering text and images in ePubs does not work on the Nook. I've read some stuff on various webpages about this, but nothing has solved the problem. Has anyone here tackled this, and if so, what's the solution?

NOTE: I am coding my books from HTML/CSS. I am not interested in using Word or other word processing tools to make my books.

Thanks!