If you’re seeing MIME type (‘text/plain’)it could be that the CSS file isn’t correctly referenced and it’s showing an error page - try visiting it directly.
Please could you share some specific details of the issue you are experiencing that may help us troubleshoot it with you, e.g. any logs/errors/output, specific/real URLs, service name/ID, reproduction steps, etc.
If you don’t want to share these details on the community forum, please feel free to raise a ticket from the “Help” or “Contact Support” links while logged into the Dashboard.