HyperText Markup Language: a set of standards, a variety of SGML,used to tag the elements of a hypertext document. It is the standard protocol for formatting and displaying documents on the World WideWeb.
CSS stands for Cascading Style Sheets. CSS describes how HTML elements are to be displayed on screen, paper, or in other media. CSS saves a lot of work. It can control the layout of multiple web pages all at once. External stylesheets are stored in CSS files.