RH Theme: Align background surfaces.

[andrew-ronaldson]

[nicolethoen]

Per the following note in the Compass/PF feedback doc from Nexus - can we make sure to double check that input background colors are made complimentary to glass effects. Feedback from initial implementation of Compass in Nexus: "Form fields with the gray background stand out as not really being cohesive with the nexus glass theme. We should consider making the background modifiable (color, etc) but still adhere to a11y compliance."