Spike: Investigate high contrast theme requirements

[andrew-ronaldson]

Goal

This spike will define the required criteria needed to build a hight contrast theme. Subsequent issues will be tracked in the theming epic

[andrew-ronaldson]

Completed with https://docs.google.com/document/d/14GFOdg0B_uq0DLq4beyaOm_x13cL4TevSQzmoFX20pk/edit?usp=sharing