I've completely fleshed out my idea for a mobile web app. I've created the mockups in Sketch 3, and have documentation of all the models and controller actions I need to make this app work.
I want to focus heavily on UX, so I'd like to quickly create an HTML/CSS prototype with full interactions so I can do usability testing, tweak and repeat before I get too deep into aesthetics, UI, data structures and all the other details that go into making a mobile web app.
I don't want to get too caught up in the details of making models, controllers and all the such (since I'll be using Rails for the app). So what tools would be best for making quick interactive mockups so I can focus most of my time on usability testing?