How to center css button on forms?

[J_R_S]

There must be an easy way to do this, but I've searched the FAQ and forum thread archives for hours and not found an answer:

By default, when Zen displays a built-in form, the "Back" and "Submit" buttons at the bottom of the form/page (whether they are CSS or non-CSS buttons) are NOT centered on the page. "Back" is usually flushed left and "Submit" is hanging out way over to the right.

All I want to do is have both buttons centered at the bottom of the form. I'd like that effect to be global for all form pages, but I'll settle for reconfiguring individual pages if necessary... but, honestly, I've tried and I can't figure it out.

Is it just one secret-handshake style-parameter buried in stylesheet.css or what?

[tony_sar]

link to your site please