Hi @oxydum,
if you use the double '' in a tiddler without a given type or with type vnd.tiddlywiki, the wiki-parser will interpret the double-single-quotes as bold formatting, which breaks your style definitions
you can do two things:
1) put your styles in another tiddler tagged $:/tags/Stylesheet , remove the <style></style> tags therefor. either make its type application/css or put a pragma rule on top that turns off all or certain wiki-parser rules
2) use your tiddler as it is, but put a pragma rule on top that turns off bold formatting (bold using ''this text is bold'' won't work in that tiddler)
a rule is set at the very top of a tiddler or at the top of a macro
it looks like this:
\rules
it follows "only" or "except"
then it follows a list of rules, see all shadow tiddlers with the title $:/core/modules/parsers/wikiparser/rules/...
...
in your case
\rules except bold
... all rules allowed except bold