[crazygringo]

Oh, interesting. I never thought of it that way. I think UX shadows are pretty universally meant to indicate the effect of floating cards rather than solid boxes (or "extruded").

But if you wanted a box to cast a shadow, I think you're better off rendering it in 3D software and then applying it as an image behind your element. Layering a bunch of guassians isn't going to look right either.

I would be interested if CSS ever decided to implement an "extruded" shadow option separate from the existing floating/gaussian one. I'm not sure there's much demand for it though? Not to mention I think it might be much more computationally expensive.