CSS
Behind the simple acronym CSS (Cascading Style Sheet) it is hidden one the main standard language of W3C.
Its history is somehow parallel to the HTML one being a complementary element. In fact, in the intensions of the W3C developers, HTML, and so its recent evolution, XHTML, should be simply seen as a structural language and nothing to do with the presentation of a document. For this aim, which is to improve the visual and aesthetic aspect of a page, the designed tools are CSSs.
The first official specifications of CSS (CSS1) is from December 1996. In May 1998 was released the second version: CSS2. No big changes, but many added from the first. CSS2 is nothing else than CSS1 plus some new proprieties, values of property and definitions for non canonical styles like those one relative to the print settings or to audio contents definition.

With CSS we are now able to set all the layout aspects into a single file, we can create different layouts according to different browsers and another very useful aspect is that we can now change the general layout of an entire website simply changing a single file and not the all .html files.