On the CSS Injector settings page (admin/config/development/css-injector/settings), there is a help text about the CSS Injector import sandbox module:
If you want to import your css injector files from dev site to production, you can use CSS Injector import sandox module.
Be aware, sandbox modules are not supported and you are using it on your own risk.
AFAIK, this sandbox module exists only on drupal.org but not for Backdrop, so I'd suggest to remove the text.
On the CSS Injector settings page (
admin/config/development/css-injector/settings
), there is a help text about the CSS Injector import sandbox module:AFAIK, this sandbox module exists only on drupal.org but not for Backdrop, so I'd suggest to remove the text.