Atahualpa: Trying to get beveled menu tabs

I am using Atahualpa 3.7.3 with the rounded tab styling for my website, however I’d like to have beveled menu tabs that look like file tabs instead. Something like this: http://www.trackmypeople.com/, with the coloring on my website.

I am a newbie and not well versed in coding, so I welcome step-by-step instructions on how to do this.

My site is http://ffladmin.netfirms.com/hermes/bosweb25b/b558/nf.ffladmin/public_html/hermes/bosweb25/

I appreciate any help you can offer.

Thanks so much