Prod CentOS core-only site work fine but local Ubuntu backup has no css loaded
Did you try the 777 recursively inside the files folder? (so it applies on files/css and files/js subfolders)

Also I would check if SELinux is enabled on your CentOS server to discard you downloaded an incomplete copy of your website due to lack of permissions. Use the getenforce command to check if it's set to permissive.
In case of necessary you can use the following command to set the context of files folder to read/write:

chcon -R -t httpd_sys_rw_content_t files