Add namespaced variables and fixes for config forms styles.
Review Request #11031 — Created May 20, 2020 and submitted
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