CSS (Cascading Style Sheets) is a programming language used to style and format web pages. It is used to control the layout, typography, colors, and other visual aspects of a website. CSS works by separating the presentation of a web page from its content, allowing developers to create a consistent look and feel across multiple pages. It is often used in conjunction with HTML and JavaScript to create dynamic and interactive web pages. CSS is constantly evolving, with new features and updates being added regularly. It is an essential tool for web developers and designers, allowing them to create visually appealing and user-friendly websites.