What role does CSS play in web design?

CSS, or Cascading Style Sheets, is primarily responsible for the presentation and visual aesthetics of a web page. It allows developers and designers to apply styles such as colors, fonts, layouts, and spacing to HTML content, effectively controlling how elements are displayed on the screen. By separating content (HTML) from design (CSS), developers achieve greater flexibility and maintainability in web design. This enables changes to be made to the design without altering the underlying structure of the content, fostering a cleaner and more efficient development process.

The other roles mentioned, such as creating content, managing server-side processing, or handling user interactions, are not functions of CSS. Content is structured using HTML, server-side processing is typically managed by programming languages or frameworks (like PHP, Node.js, or Python), and user interactions are generally handled through JavaScript, which allows for dynamic changes to the web page in response to user actions. Thus, the distinct role of CSS as the tool for designing and styling web pages solidifies it as the correct answer.