Looks great on mobile. I tried to look at the HTML source code to check if you where using front-end framework but I wasn't able to find any.
How did you build it?
ClojureScript with Enfocus (https://github.com/ckirkendall/enfocus/) in the front-end, and Clojure with Enlive (https://github.com/cgrand/enlive) in the backend. It's not a SPA. I started it a while ago, before React/Om. If it were now I would write it as a SPA and use some React wrapper, probably Rum (https://github.com/tonsky/rum).
As for HTML/CSS, no framework at all. I'm interested in simple, minimalistic, innovative design, and I don't think frameworks help to achieve that.