What is the primary function of CSS in web development?

The primary function of CSS (Cascading Style Sheets) in web development is to control the layout and design of a web page. CSS is responsible for specifying how HTML elements are displayed on the screen, allowing developers to apply styles such as colors, fonts, spacing, and positioning. This separation of content (HTML) and presentation (CSS) enhances design flexibility and enables easier maintenance of web pages.

By using CSS, developers can create visually appealing designs consistent across different pages and devices. It ultimately improves user experience by making websites more attractive and easier to navigate. CSS also supports responsiveness, enabling websites to adapt to various screen sizes and orientations, making it essential for modern web design.

The other options, while relevant to web development, do not reflect the primary purpose of CSS. HTML structures the document, JavaScript is typically used for creating functionality, and server responses are managed by server-side languages and protocols rather than CSS.