Change 532729 had a related patch set uploaded (by Pablo Grass (WMDE); owner: Pablo Grass (WMDE)):
[mediawiki/extensions/Wikibase@master] bridge: use padding-less panel for bridge dialog

https://gerrit.wikimedia.org/r/532729

@Michael Does https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/532729 work in our favor in that regard?

In T230895#5442250, @Pablo-WMDE wrote:

@Michael Does https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/532729 work in our favor in that regard?

Yes, I think this does what we need 👍

I looked at the patch as it evolved and tried to rebase it. In the mean time changes by the same author were merged (for T230328) into the main line which take a different approach to a somewhat similar challenge so I don't quite know which is the desired one...

So maybe first things first: do we agree that at default base font size (16px), the size of the padding should be a computed value of 16px?
We probably don't want to express this in px but use a relative unit instead. Do we consequently want this padding to be relative to the font-size of this element (arguably an inherited one) or the base font size? In my suggestion I went with the first option because that's what happens in OOUI (1.14285714em, not rem).
Based on that decision we can talk about different ways to reach that goals and possible functions to made the code more convenient/elegant (e.g. a calculate-em() function).

A side note: I don't see much value in putting all variables in the _variables file, especially so if they are only used once and carry overly specific names (effectively ruling out even future reuse).