HTML, or HyperText Markup Language, tells the browser how to display text and images on a web page. Think about how you create a document with a word processor.
Whether you use Microsoft Word, WordPad, Apple Pages, or another application, your word processor has a main window in which you type text, and a menu or a toolbar with multiple options to structure and style that text. You can create headings, insert pictures, underline text, and much more. Similarly, you can use HTML to structure and style text and other elements that appear on a website.
Markup language documents, such as HTML documents, are just plain text files. Unlike documents that can be viewed only with the word processor used to create the document, you can view an HTML file using any web browser on any type of computer.
HTML files are plain text files that appear styled only when viewed with a browser.
CSS, or Cascading Style Sheet, styles HTML elements with greater control than HTML. Take a look below. On the left is a Facebook page as you’d see it in your browser. On the right is the same Facebook page without the CSS styling; all the images and text appear left-justified, borders and shading disappear, and the text has minimal formatting.
Before AJAX, the browser would display new data on a web page only after waiting for the entire web page to reload. This technique slowed down the user experience, especially when viewing web pages with frequent real — time updates, such as news, sports updates, and stock information. With AJAX, the browser could communicate with a server in the background, and update the current web page with new information.