I would use an image if I were you as there are a couple of problems I can think of with doing it in CSS.

Firstly - Accessibility: People using text browsers will see the description twice, which can be annoying. Likewise anyone using an Aural browser will hear the words spoken twice, again annoying.

Secondly, and probably most importantly for most people [at the moment anyway] - the search engines will at least down grade your site [and possibly ban it] if they think that you are keyword spamming - and the product description is an important keyword.

Just my opinion.