CSS not working in Django admin: The resource from [css file url] was blocked due to MIME type (“text/html”) mismatch (X-Content-Type-Options: nosniff
I got the error

Refused to apply style from '' because its MIME type
  ('text/html') is not a supported stylesheet MIME type, and strict MIME
  checking is enabled.

because one of my Cloudflare manually created firewall rules blocked CSS URLs.
I discovered this when opened my Cloudflare dashboard and sow that firewall rule was applying 'JS challenge' to the URLs like https://[my-website]/static/admin/css/.
So if your website can not load some resources and you get the error about MIME type please check your Cloudflare dashboard or try to temporary disable it.
Django admin is displaying without CSS because of the error: 
The resource from “my-website-address/static/admin/css/responsive.css” was blocked due to MIME type (“text/html”) mismatch (X-Content-Type-Options: nosniff).
The CSS url I can open in my browser and it looks fine.
What can I do to fix CSS displaying for standard Django admin interface?