Use primitive operations
Using methods for basic operations uses additional system resources. The interpreter must first resolve the objects and then the methods just to run the simplest of operations.
Therefore, avoid them as much as possible.
Minimize the number of CSS files and compress them
Minimize the number of CSS files to reduce the number of HTTP requests. If several style sheets are used on all of the website’s pages, concatenate them into one single file.
Some CMS and frameworks offer ways to do such optimization automatically. The HTTP server can also be configured to compress and reduce the size of style sheets (see best practice #79).