Type the location of the cascading style sheet file you want to use for this portal site. If the file location is a local ...

Type the location of the cascading style sheet file you want to use for this portal site. If the file location is a local relative path (for example, /_layouts/1033/blue.css), you must copy the cascading style sheet file to that location on each front-end Web server. For better performance, it is recommended that you copy the file to the _layouts folder on each front-end Web server.