RoboHelp x5 rewrote CSS as well. I'm pretty sure they think
it's a feature.
The workaround I developed involves authoring/editing the
.css files outside RH, keeping them under version control, and
reverting them whenever RH tries to change them, plus copying clean
.css files over the rewritten ones after projects have been
generated.
Note that for every stylesheet fname.css you have, RH will
create a supposed "Netscape" version of the stylesheet called
fname_ns.css. Again, I'm pretty sure they think this is a feature.
Unless you like the way the _ns.css version looks on
Netscape/Firefox/whatever, you will want to copy your clean
fname.css over fname_ns.css as well.
Amy