DHTML, or Dynamic HTML, consists of HTML, CSS, and JavaScript. DHTML makes it possible for a web page to react and change in response to the user's actions.
HTML defines Web sites content through semantic tags (headings, paragraphs, lists, …) while CSS defines 'rules' or 'styles' for presenting every aspect of an HTML document. These include font size, font color, background color, background position, layout, etc. JavaScript defines dynamic behavior through programming functions for interaction with the user and to handle events such as clicking a button.