Use accessible colors

bserem → changed the visibility of the branch 3521710-use-accessible-colors to hidden.

bserem → changed the visibility of the branch 3521710-use-accessible-colors to hidden.

bserem → changed the visibility of the branch 3521710-use-accessible-colors to active.

@gkffzs adding another environment type ('lo', 'dd') should be a different task and not part of this one.

Here I am only trying to make sure that the current codebase is a11y-compliant

Thanks for your suggestions.
There is another issue to consider. The background behind the indicator text was lightened, which could affect a11y too. Instead, I darkened the background.
I've also added a new environment 'de' for dev or development. Local or ddev would be the default fallback.
Feel free to review 3.0.x-dev