CSS stand for Cascading Style Sheet. CSS3 is the new standard for CSS. It is not yet supported by all of the main browsers. Some browsers only support certain CSS5 styles. One of the new properties of CSS3 is gradients. This will allow designers to use gradients as a “color” instead of having to resort to a image to create gradients. It allows you to create linear or radial gradients as well as repeating of both kinds. Another great new property is multiple backgrounds. This lets designers stack different images as backgrounds of the same element. Each layer can be moved and animated independently. Another feature that is only available is webkit browsers was masking. It would allow you to mask any images you put on your website either with a CSS3 gradient or PNG file. I think this will definitely be a property that will be implemented in the near future because it seems to have so many possibilities.
Here is some of my research is you want to know more: