HTML (HyperText Markup Language) is the fundamental markup language used to create the structure and content of web pages. It defines the semantic elements of a webpage, such as headings, paragraphs, links, images, tables, and forms, which together form the skeleton of a website. HTML uses a tag-based system, where each element is wrapped in opening and closing tags to specify its role in the document. With HTML5, modern features like audio, video, canvas, and semantic tags were introduced, enhancing accessibility, multimedia support, and cross-platform compatibility. CSS (Cascading Style Sheets) is the language responsible for styling and designing web pages. It allows developers to control layout, colors, typography, spacing, transitions, and animations. CSS follows the principle of separation of concerns, ensuring that structure (HTML) and presentation (CSS) remain independent, which improves maintainability. Modern CSS provides powerful features such as Flexbox and Grid for responsive layouts, media queries for adapting designs across devices, and variables for consistent styling.