Wow CSS is becoming more and more like a programming language. Good job on Firefox for pushing the boundary.
One thing though. The calculations don't seem very semantic. To calculate something as simple as height/width, you need a long calc(var(height)/var(width));
Maybe w3 can implement CSS variables with special characters like in PHP.
Using $ to identify variables was proposed in the CSS working group. It was ruled against in order to keep that syntax free for future developments (e.g.g SASS-like macros).
One thing though. The calculations don't seem very semantic. To calculate something as simple as height/width, you need a long calc(var(height)/var(width));
Maybe w3 can implement CSS variables with special characters like in PHP.