HTML (Hypertext Markup Language) and CSS (Cascading Style Sheets) are the cornerstone technologies for web development. HTML provides the structural foundation of a web page by defining elements such as headings, paragraphs, links, and images. It acts as the skeleton of the page, outlining where content and components should appear.

CSS complements HTML by managing the visual presentation of the web content. Through CSS, developers can apply styles such as colors, fonts, and layouts to the HTML elements, creating a visually engaging experience. CSS also ensures that web pages are responsive and adapt smoothly to different screen sizes, enhancing usability on both desktops and mobile devices.

Together, HTML and CSS enable the creation of well-structured, visually appealing websites that offer a seamless user experience. They are integral to developing modern, user-friendly websites and applications, forming the foundation upon which advanced functionalities and designs are built.