According to the W3C website, the process of CSS started in 1994. The Web was starting to be used more in things regarding electronic publishing. It was missing something though. There was no way to style documents. There was no way to describe certain layouts and formats, so a style sheet language needed to be created. It wasn’t an entirely new idea. Tim Berners-Lee had wrote a sort of browser/editor, but it wasn’t universal. Before CSS, the style sheets were individually designed to best display to its users. This was not an efficient way to style documents.
In 1993, the NCSA Mosaic came out. It helped to popularize the Web even more, but limited the styling options in which people had. Web page writers were also having trouble with not being able to design their pages in the ways that they wanted to. Then the first draft of Cascading HTML Style Sheets was created by Håkon Wium Lie. People responded to it, as well as other styling language ideas. Argo, a styling sheets idea, combined forces with CSS and they worked to make CSS better. Bert Bos was the creator of that. That version of CSS doesn't resemble that of the one today, but it did lay the foundation for it.
CSS had competition such as Pei Wei’s language and DSSSL. But CSS had a feature that none of the others had. It took into account that the style of the document couldn’t be designed by just the reader, or just the author, it needed to be a combined effort. In 1994 and 1995 CSS was proposed at the WWW conference. In 1995, the World Wide Web Consortium (W3C) came into operation and became very organized. The W3C set up an HTML Editorial Review Board and they looked to ratify style sheets. ICSS was finally approved and level 1 of CSS emerged in December of 1996. In February of 1997 it got its own working group in the W3C. Level 2 came out in 1998, and level 3 came out in 1999.
CSS also grew bigger because of browsers. They supported it from a commercial stand point and prevented it from being just for academic interest. Microsoft and Netscape use CSS. CSS has grown a lot, and is very beneficial. Everyday people, companies, programmers, and more use it to easily style and format documents. It is universal, and has made the process of customizing Web pages much easier. It has also made transition between the author to the reader of the Web page seamless, and made both sets of people happier.Link to further reading on the subject of CSS History.