This absolutely sucks in every way. The icons suck, they aren't clean, clear, flexible, or well made. The styles suck, they are too basic to even be useful - we can all put a 1px border or border radius on an element. And it's not innovative in any way, web designers have been doing this for years, except with actually good icons and css styles.
I'm genuinely surprised that this made it to the front page of hacker news. That being said, I still think Nick La is a great designer.
This is why I'm completely behind efforts like Twitter's Bootstrap Font Awesome to standardize an internet icon set.
Why do I have to hear about every front-end web dev's effort to reinvent the wheel? Why are users forced to relearn a new visual language to accomplish the exact same task on every website?
There are some pressed classes defined but I don't think you can dynamically add them when the button is :active through CSS only.