Fix options per line display of custom fields

Updates the css with changes made in https://github.com/civicrm/civicrm-core/pull/30162

Before:

After

Thanks @jitendra so much for this PR. I can confirm it works as intended.

It does get wobbly at smaller sizes, I think an issue with Flexbox over Grid. I'll try to see if there are any other fixes for that.

Am just merging this for now as Finsbury Park will soon be deprecated in favour of its replacement: RiverLea - HackneyBrook (which looks the same but uses a rewritten base).

mentioned in commit a38be70b

merged