Dear Denis,
- You've posted in French on an English language forum - please see my moderator reply above.
- The correct code is https://gitlab.com/jezhops/moodle-theme_adaptable/-/blob/MOODLE_38/lib.php#L578-642 - the code you have posted has been adapted from the Essential theme given 'theme_essential_serve_css($args[1]);' thus wrong. Therefore everybody, DO NOT follow this advice it is WRONG.
- If something is broken with your site, then please demonstrate this with Moodle and theme version.