HTML (HyperText Markup Language) and CSS (Cascading Style Sheets) are fundamental building blocks of web development, used for structuring content and designing web pages respectively. Coursera's HTML and CSS catalogue empowers you to build interactive, responsive, and user-friendly websites. You'll learn the principles of web design, mastering HTML for organizing website content and CSS for applying styles and layouts. By exploring topics ranging from basic syntax and selectors to complex responsive design techniques, you'll develop a strong foundation in web development. This knowledge will enable you to create websites that deliver an optimal user experience, adapting to various devices and screen sizes.