CSS and image sprite

Hi, I would like you to sprite the images of my menu into CSS to increase performance of my site as well as some advices on how to optimize my CSS files to get a good grade at GTmetrix. Attached there is the file you will have to sprite and modify the css in order to make it work. Here the link to the menu: [login to view URL] If you show good results, we can start an optimization project for the whole site based on GTmetrix advices. Thank you.