What are Cascading Style Sheets (CSS) used for?

Cascading Style Sheets (CSS) are specifically designed for manipulating and controlling the appearance of web pages. CSS allows web developers to separate content from design, meaning they can define styles for various elements within an HTML document, such as fonts, colors, spacing, and layout. This separation enhances the flexibility and maintainability of web pages, as changes to the design can be made in the CSS file without altering the underlying HTML structure.

While network security settings, data storage in databases, and compiling programming languages are important aspects of computing and information technology, they are not related to CSS. Network security relies on different protocols and settings; databases use languages like SQL for data manipulation; and programming languages require compilers or interpreters to convert code into executable formats. Consequently, the unique role of CSS in web design clearly establishes it as the correct answer.