Hi,
You can rewrite those urls as such like so:
rewrite ^/css/css.css$ /template/webroot/css/css.css last;
rewrite ^/img/img.jpg$ /template/webroot/img/img.jpg last;
rewrite ^/css/admin/css.css$ /admin/webroot/css/admin/css.csslast;
rewrite ^/img/admin/img.jpg$ /admin/webroot/img/admin/img.jpg last;
You should also take a look at:
http://wiki.nginx.org/HttpRewriteModule
http://nginx.org/en/docs/http/converting_rewrite_rules.html
For more info ;)