Customize error pages

[teolemon]

Story

Is there a way to show our own branding in case of error ?
https://auth.openfoodfacts.org/realms/open-pet-food-facts/account?referrer=ProductOpener&referrer_uri=https%3A%2F%2Fworld.new.openpetfoodfacts.org

[hangy]

There's an error.stl theme file in the base theme, so it should be possible to override it in the off theme.