Dave,
I'm guessing you tried to add your new style to the style
sheet using the Format > Styles dialog. Most of RH's styles are
paragraph-level. The character-level styles are for things like
DHTML text. You can edit your .css file in a text editor, but if
you go that route, do so with a copy of your project first. RH has
its own mechanisms for coding styles in the .css file (open the
file in Notepad and you'll see what I mean), and I manually enter a
style only when I don't have any other option for what I want to
do. You can find all kinds of info online about how to create
styles in CSS.
Another caveat here is that RH seems to freely use the
<span> tag, which is the element you'd use for most
character-level styles. If you start specifying a span class for
bits of text within paragraphs, RH may get confused, and the
<span> tags may start proliferating like rabbits in your
code. I have seen <span> tags pop up like crazy in RH X5 and
6, but I'm still only trying out RH7, so I don't know if it's a
problem there.
So like Peter Grainge may say here, back up your project and
be careful if editing styles manually.
Hope this helps,
Ben