CSS, or Cascading Style Sheets, serves as the aesthetic layer of the web, bringing life and personality to HTML documents. Through CSS, developers can control the visual presentation of web pages, including layout, colors, fonts, and animations. By separating content from design, CSS promotes clean and modular code, facilitating easier maintenance and scalability. With its wide range of selectors, properties, and values, CSS empowers designers to create visually stunning and responsive websites that captivate and engage users across various devices and screen sizes.