base URL for external stylesheet ?

so, if my original structure is :

Code:

- codeigniter (.env  app  system writable …)
- public
     - assets (css img js)
     - index.php

You would just do :

Code:

- codeigniter (.env  app  system writable …)
- public
     - assets (css img js)
     - demo
          - index.php

...leaving the assets on the root of "public" folder ? I didn't find other solutions :
- Either I leave assets on the root
- or I have to change all URL in my CSS and add "demo/" (even if my baseURL and index.php is "demo/")