rewrite rule custom.php to custom.css

[AndriesLouw]

If you want it mod_rewrite style (so no 302 Temporary Redirect header):

location ^/wp-content/themes/mytheme/assets/css/ {
    rewrite custom.css custom.php;
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,220792,220906#msg-220906