HyperText Markup Language (HTML) is the language behind most Web pages. The language is made up of elements that describe the structure and format of the content on a Web page.
Cascading Style Sheets (CSS) is used in HTML pages to separate formatting and layout from content. Rules defining color, size, positioning and other display aspects of elements are defined in the HTML page or in linked CSS pages.
The main purpose of Ajax is to provide a simple and standard means for a web page to communicate with the server without a complete page refresh.