CSS frameworks are crucial in modern web development, offering tools to build responsive, user-friendly, and consistent web interfaces with reduced development time. They provide pre-written CSS and HTML files that ensure cross-browser compatibility, maintainability, and performance optimization. Some popular frameworks include Tailwind CSS, which is highly customizable and optimized for performance; Bootstrap, known for its comprehensive UI components and ease of use; and Foundation, which emphasizes accessibility and customization. Each framework has unique features and benefits, catering to different project needs, whether for small personal websites or large enterprise applications. Testing for browser compatibility remains essential, with platforms like LambdaTest facilitating cross-browser testing to ensure seamless performance across various environments. Overall, selecting the right CSS framework depends on the specific requirements of a project, including design preferences, functionality needs, and development constraints.