eXo Portal 2.0 early success is also based on its great art work and web design. 

To achieve such a quality, we employ 5 professional web designers that spend their time making greats skins for us and our customers. 

This of course implies the use of many images in the portal page.  Unfortunately, this may impact the page processing time if each image is served through a single HTTP request.  Furthermore, it also increases the number of hits on the server which consumes CPU and lower the number of concurent users you can get. 

Hopefully, there exist a method that allows to use several images within the page but to request them thanks to a single CSS request.  This technic is called CSS sprite. 

The idea is quite simple and leverages advanced CSS 2.0 features.  We append into a single image several icons that will then be used in the css background code and relatively positioned using the following syntax: