Without knowing much about the specific error, I'm going to say you should check file permissions (that's usually what "forbidden" errors are about in my experience).
Go to your html root directory (/srv/www/website.com/public_html/, it looks like) and type
then make sure all the files belong to the user the web server is running under. They should have a user and group that looks appropriate to your web server - I haven't used that one specifically. Or they might be root, I've seen that before. The SELinux context (you'll only see that with the first command) should be something like
It might not be exactly that but if it's got "http" in there or otherwise looks web-related you're probably okay. Don't be alarmed if it doesn't show up; I'm not sure that Ubuntu would even force that. You might only get the user/group permissions.
Including the SELinux context, you should get results something like this:
drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_rw_content_t:s0 css
drwxr-xr-x. apache apache unconfined_u:object_r:httpd_sys_rw_content_t:s0 downloads
though again, maybe not exactly. With the second command it would look more like this:
drwxr-xr-x. 2 apache apache 4096 Aug 19 00:41 css
drwxr-xr-x. 3 apache apache 4096 Jun 26 22:36 downloads
Once again, the user and group might not necessarily be apache. If it's something related to your web server, or possibly root, that's good to.
If the user and group are wrong, you can change them with:
chown -R user:group folder
If the SELinux context is wrong (if it's not even there you probably don't need to worry about it) you can fix it with:
chcon -R -t httpd_sys_content_t /srv/wwww/website.com/public_html/
It might also be an issue with a missing module or something for your web server. I've never used ngnix before, but I remember when using lighttpd instead of my usual apache I had this very same unexpected difficulty with php files. I had to install a module and make a minor configuration change. Unfortunately I can't offer any advice beyond that - like I said, I haven't used ngnix specifically.