What is the function of CSS in web development?

CSS, or Cascading Style Sheets, plays a crucial role in web development by allowing developers to add styles to a website. This encompasses a wide array of visual elements, such as colors, fonts, layouts, spacing, and overall presentation of content on webpages. By separating style from content, CSS makes it easier for developers to maintain a consistent look and feel across various pages of a site.

Applying styles through CSS not only enhances the aesthetic appeal of a website but also improves usability and accessibility, ensuring that users have a pleasant experience while navigating the site. The ability to use classes and IDs further allows for targeted styling that can adapt to various screen sizes and devices, catering to responsive design needs.

The other choices, while related to web development, do not accurately describe the core function of CSS. Performance is more closely tied to client-side scripting or server-side optimization. Structuring HTML code is primarily the job of HTML itself, whereas scripting application behavior is handled through JavaScript or other scripting languages.