Impossible / Not clear how to change TopBar background colour

[artyrcheek]

Issue summary

We are advised in the polaris docs to "Use a top bar color with a color difference greater than 100 (calculated using the Euclidean distance) from the Shopify admin top bar. You can check your color with this color difference checker." However Im not sure if its possible / Its not clear / there are no examples to edit the TopBar component background colour see https://stackoverflow.com/questions/65961274/setting-topbar-background-colour-in-shopify-embedded-app

Expected behavior

There are examples on the polaris docs on how to do this

Specifications

• Are you using the React components? (Y/N): Y
• Polaris version number: latest