Standardize how and what units are used

This is necessary so that prosilver and the new theme will follow the same standards. Set in our stylelint file.

Basically im converting all the ems to px values for prosilver. I am also converting all line-heights to pxs first to make them all consistent.

We can convert from pxs very easily late, we can not easily move from ems however and everything needs to be the same units to move forward.

There is no longer a downside in any browsers that we support to using px for everything BTW they all support px scaling.