You can surely use CSS to make the buttons look however you'd like. If you're asking if there's a setting where you can say "Look like Mac", then the answer is no. I'd recommend using Adobe Photoshop to make the button how you want it to look, then use CSS to stylize the button.
Run a Google search for "css buttons" and you can find several tutorials. Hope this helps!
common simple interactive controls should probably be left alone as much as possible, even apple recommends this...
while looks aren't important, you should not want to change the behavior. People who depend on assistive technology to view the web are expecting certain keys, clicks, and generated clicks to do certain things.
Also, regular users expect things to be a certain way.
you never hear anyone say "wow, that non-default behavior i wasn't expecting sure makes this app a delight to use"...