HTML is responsible for a website's fundamental structure and formats the contents of web pages (headings, paragraphs, links, and images). The visual presentation of a web page's content (fonts, colors, and layout) is handled by CSS. Since Javascript enables interactivity and allows dynamic functionality, it is responsible for how pages behave. These three web technologies are essential for front-end development since they determine UI and UX. Nevertheless, only Javascript can be used in back-end development because it can manage server-side operations like data storage and retrieval.