CSS 3 is the latest version of the Cascading Style Sheet specification and is responsible for the presentation of the elements.
Using CSS means that content on the web page can be separated from the presentation making it possible to change the styles so that the same content can be presented with a different look.
CSS 3 is not one single specification but is made up of a number of modules. There are over 50 of these modules each of which are in various states of status and stability. From the point of view of the web developer the majority of attributes that you will want to use are available on the majority of the latest web browsers. However, there will be some features that will not work on certain browsers and there are sites such as:
which show browser compatibility.