[Public interface]: OAC UI updates based on WCAG 2.1 audit (medium priority levels)

[aturner]

Propose that we focus on issues flagged as medium priority for MVP: https://docs.google.com/spreadsheets/d/11Na8eMq6tM65Lg_gSg1bsybJvlMXZ0tZjabFOzY8Vgk/edit?usp=sharing

Builds on #349