Base Appearance value & indicator pseudo prep for VF2F

Hey everyone,

I would like to move forward with interoperable pseudo elements for
checkbox/radio and then more controls/components beyond that where there is
interest. I want to raise these again at the upcoming VF2F but also want to
ensure that any additional questions folks have been addressed prior if I
can; as I addressed the questions/concerns raised from the last F2F
(appreciation to Jen & Florian for their feedback).

If you all can review the issues and let me know if you have any additional
questions.

I'll be discussing them in the following order:

   - base appearance value <https://github.com/w3c/csswg-drafts/issues/5998>
   (required for any interoperable controls discussion checkbox & mozilla is
   interested in standardization of range
   <https://github.com/w3c/csswg-drafts/issues/4410#issuecomment-783022435>)
   - indicator <https://github.com/w3c/csswg-drafts/issues/5914>
   (checkbox/radio pseudo element)
   - Explainer
   <https://github.com/salesforce/standards-explainers/blob/master/indicator-psuedo/explainer.md>


Thank you,
Greg