The config forms codebase was one of the earlier ones to adopt our

modern CSS component naming styles, but it didn't adopt the namespaced

variables along with it. We had some legacy variables, but if anything

external components wanted to size anything according to the config

forms definitions, they'd have to hard-code values.
This change moves most of the variables over to that style, and

introduces a whole bunch of new ones. These can be used by other

stylesheets to better fit in with a config forms page.

Tested various config form pages with these styles. Didn't see any

regressions.