HTML provides the basic structure and content of a webpage. CSS handles the visual presentation and controls elements such as the layout, colours, and fonts. JavaScript adds interactivity and dynamic features, which enables features such as user interface updates and event handling. These three aspects are the core of front-end development, focusing on what users see and interact with directly in their web browser. In terms of back-end development of web design, HTML, CSS and JavaScript involves server-side logic, databases, and the infrastructure that powers the website behind the scenes.