What you do next is up to your preferences. I think it is worth it to transform your sketches to wireframes. In most of my cases that was still a more open process than fitting the sketches into CSS directly - especially if you have designers, business people and coders involved.
One possible solution for wireframing that was already available in 2012 is Illustrator or InDesign. Both have global colors, symbols for reusable content and are vector-based so you can scale it for your responsive designs.
There are less good ressources on wireframing with Illustrator, but I found these two most helpful:
- http://www.designsprint.net/ - http://design.tutsplus.com/articles/10-tips-for-building-wir...