I would not encourage the use of PX at all - no need for anything to be PX. Why not use REMs? Combines the best of both EMs and PX, and since most developers use SASS/LESS, the calculation for REMs isn't an issue. No need for a base body font size either when using REMs, as this would defeat the point.
Page Title
Code Standards
URL
https://docs.modx.com/revolution/2.x/developing-in-modx/code-standards
Issue or Suggestion
I would not encourage the use of PX at all - no need for anything to be PX. Why not use REMs? Combines the best of both EMs and PX, and since most developers use SASS/LESS, the calculation for REMs isn't an issue. No need for a base body font size either when using REMs, as this would defeat the point.