Understanding the how and why code does what it does and limitations of what can be done is essential to writing clean, semantic markup. With that being said, a lot of HTML & CSS frameworks have been surfacing lately to assist even the most novice developers to create their own coded prototypes. This is wonderful for those designers who want to test quick interactions and flows with users or even understand how structure and style tie-in closely with one another.
I am a strong believer that designers that can code up what is in their head make for better designs in the end. However, taking the plunge to understand code and how it all works is a bit daunting to some. These frameworks make producing testable prototypes as easy as " copy, paste. "
Here’s a list of a few of them: