The main advantage of CSS is that you can change the color and appearance of components without using a graphics package, and they might scale better. But that's about it.
It was a technical exercise rather than a proof of concept. The icons themselves are very simple and limited. I wouldn't recommend using CSS in this way for production work (other than perhaps for very simple arrows).
I'm not sure some simple arrows can be achieved with unicode characters...nor would you want a screenreader to pay attention to what is purely presentational.
The main advantage of CSS is that you can change the color and appearance of components without using a graphics package, and they might scale better. But that's about it.
It was a technical exercise rather than a proof of concept. The icons themselves are very simple and limited. I wouldn't recommend using CSS in this way for production work (other than perhaps for very simple arrows).