Cascading Style Sheets, or CSS, is the language that controls how web pages look. It lets authors set color, layout, spacing, and fonts separately from the HTML that defines a page’s content and structure. This separation means the same document can be restyled without touching its markup.
The idea traces to Hakon Wium Lie’s 1994 document, “Cascading HTML Style Sheets — A Proposal,” dated 10 Oct 1994. It introduced the defining mechanism: a “cascade” in which style rules from multiple sources combine with weighted influence, balancing what a document’s author wants against what its reader prefers. That cascade is the feature the language is named for.
CSS became an official web standard when the World Wide Web Consortium published “Cascading Style Sheets, level 1” as a W3C Recommendation on 17 Dec 1996 (later revised 11 Apr 2008). CSS1 gave browser makers a common target so that styling would behave consistently across implementations.
The original CSS1 document is now marked a Superseded Recommendation, with newer CSS specifications recommended for fresh adoption. But the model it set out, rules cascading from author and user style sheets to decorate structured HTML, remains the foundation of how the web is designed today.