Mark [1] heard my tales of woe about style sheets and mentioned Amaya, [2] the reference implementation by the W3. [3]
I check, and indeed, Amaya supports HTML 4.0, MathML, CCS1, XML and a host of other WWW alphabet soup standards. The source code requires Motif, and lacking that, I decided to download the precompiled version.
It works, in that it runs on my system.
.
But it doesn't support CSS correctly either.
Sigh.