Utility-First CSS is a design approach that emphasizes the use of small, reusable classes to style elements directly in HTML. Instead of writing custom CSS for each component, developers apply predefined utility classes that control specific styles, such as margins, padding, colors, and fonts. This method promotes consistency and reduces the need for complex stylesheets. Frameworks like Tailwind CSS exemplify Utility-First CSS by providing a comprehensive set of utility classes. This approach allows for rapid prototyping and easier maintenance, as changes can be made directly in the markup without altering separate CSS files. It encourages a more modular and efficient way of building user interfaces.