I tried FireBug but it kept causing crashing and spinning out of my FireFox so I uninstalled it. (FireFox has gotten increasingly "sucky" in the past 5 years...)
I guess I could have viewed the source, but usually professional websites have so much junk in their code - thanks to hidden stylesheets and everything being created in DreamWeaver that it is IMPOSSIBLE to follow?! (Apparently none of the designers were SitePoint members?!)
Background images or JS. They've created some tiny top divs with rounded background images for the top, and bg image on each main div for the bottom.
They've used bg images. Again, it could be done with CSS3 (not supported by all, of course) or JS.
Oh. They did such a good job I wasn't sure since it just looks like a thin grey line drawn around things. (Had they had solid rounded corners - like Tabs - then I would have figured that out.)
It still can be done, but requires some more trickery. The dreaded sliding doors is the general flavor.
To be clear, I didn't mean Fluid or Elastic inside the boxes, I meant how well do those boxes - with fixed dimensions - play in a Fluid or Elastic layout where things move.
I suppose if you know what you are doing it isn't a problem, but who knows?!