By "browser-safe", I assume you mean accessible? I'm afraid that's not
an issue that can be solved by applying a different theme, because
TiddlyWiki is powered entirely by JavaScript.
We recently had a discussion on using TiddlyWiki for regular websites:
http://tinyurl.com/229a6u
(http://groups.google.com/group/TiddlyWiki/browse_thread/thread/6fecf9a673f5f140)
Also see this (yet incomplete) page on the community wiki:
http://www.tiddlywiki.org/wiki/TiddlyWiki_As_a_Website
These issues are being worked on, but there's no ETA yet.
-- F.
For those not familiar with the term, Wikipedia has an article on (web)
accessibility:
http://en.wikipedia.org/wiki/Web_accessibility
-- F.