CSS is not meant for this use.
The idea is to style a particular phrase throughout the whole site without having to use tags on every single page the phrase is being used. So I guess going with jQuery or PHP would have to do the trick.
Am going to guess that this is because you are building the site off a CMS and do not want to input the tags at data entry, other wise ti really doesnt make much sense.
As Pullo said, .js (or jQuery) could accomplish this ( by searching the content and then wrapping the tags around it). So in essence you are still adding tags.. just the hard way.
I would advice to use PHP , instead, to search/ replace phrase with tags around it during output. Plus that way your styling would remain intact if users have .js turned off, not to mention (again) that proper tag usage has SEO/semantic benefits.