@imorente the reasons for using `px` are consistency with existing CSS and the fact that `rem`s and `em`s can cause half-pixel boundaries, which are undesirable. I have mixed feelings - those are both significant issues, but the accessibility problem is a hard one to ignore. For now, I think we should stick with `px` for the simple reason that we shouldn't make a transition to relative units ad-hoc, even if we do end up using them at some point in the future.