CSS or cascading style sheet is one of the revolutionary concepts which changed the concept of web design to a great deal. If you are looking at any good looking website, then it is CSS who is behind it. If you are looking at a bad looking website, chances are CSS is also behind it but the developers or designers used this tool in a wrong way. That is the power of CSS. Today everyone is using CSS to make their site more attractive.
Before CSS came into play, web design was in primitive stage and people hard-coded the styling rules. CSS made possible for more of a generalized manner where you will write styles for elements or group of elements rather than hard coding it in the page itself.
For example, with just one line, you can change the whole color of the links in the whole page by CSS or as matter. Of fact, you can change any element attribute via CSS. Not only that, you can also put conditional styling in CSS. For example, you could let's say, change the color of the last paragraph only or font style for specific words, etc via CSS.
With the CSS 3, the world has entered a new era in web design. With CSS 3, the sky is only the limit. And people are making new fields where it could work more and more. This CSS can change the whole outcome of a technology and thus, be relevant to the outside changes. This is how CSS could influence the developers.