The style sheets allow you to define your platform's global visual style.
Illustration 37: Administration – Stylesheets configuration
Since version 1.8.7, it is possible for you to create your own stylesheets and send them to the server. In order to do this, download a copy of one of the existing styles in chamilo/main/css/ and change the name of the recovered directory (on your computer, not on the server). Modify the style to your taste. Once you're happy with the changes, send the directory to the server as a .zip file and give it a name that corresponds to your portal.
Illustration 38: Administration - Stylesheets upload
Then, select the style in the drop-down list. If you're happy with it, click the Save settings button to apply it as a default style for your portal.
Check the video here for the complete procedure: https://www.youtube.com/watch?v=GA0Yw8AVp8U