CSS Sprites it is a common technique in web development. Are necessary in situations if we want to reduce your server load. Instead of uploading multiple images, we only have the desire to generate a single. Through the css change what becomes visible / invisible inside the div / tag. Of course the image is always used as background. In the examples below refer to the image is not repeated either in the x axis or the axis of y. In the case of terms such images have to be made new images.
Os exemplos que se seguem dizem respeito ao site http://www.rtp.pt e em que usei este método