As part of experimentation day we're setting up an experimental CSS variables editor on test instances (specifically for the [defaultcontent](https://github.com/greenpeace/planet4-defaultcontent) instance, but can be used on others too). This is enabled with a feature toggle that is off on production instances.

Relevant PRs:

https://github.com/greenpeace/planet4-plugin-gutenberg-blocks/pull/495/files

https://github.com/greenpeace/planet4-master-theme/pull/1173/files

https://github.com/greenpeace/planet4-master-theme/pull/1320 

https://github.com/greenpeace/planet4-docker/pull/61