What is the purpose of style sheets in web design?

Style sheets, particularly in the context of web design, are primarily used to dictate the presentation of web pages. This includes aspects such as layout, colors, fonts, spacing, and overall visual aesthetics. By using Cascading Style Sheets (CSS), designers can separate the content of a website from its visual style, allowing for more efficient updates and a cleaner structure.

When style sheets are applied, they enable web designers to create a consistent look and feel across multiple pages of a site without needing to rewrite the same styles in each HTML document. This not only simplifies maintenance but also enhances the usability of websites by enabling rapid redesigns and improved accessibility.

The other options provided do not align with the primary function of style sheets. Style sheets do not define functionality or manage user data and interactions; that is typically handled by programming languages like JavaScript. Additionally, while efficient style sheets may contribute indirectly to performance, they are not designed specifically to enhance file transfer speeds. The core purpose remains firmly rooted in shaping how web content is presented to users.