HTML describes structure of web page using markup it is a file containing Hypertext Markup Language. An HTML document is a text document it is very easy to read in a Web browser to make effective presentation and then rendered on the screen it provides plexible way to design web page. It is platform-Indipendent because it can displayed on any platform.
CSS stands for Cascading Style Sheet, it is used design HTML tags for developing a web page. It is style sheet language which used to completely change the look and formatting of the web pages with few changes in CSS code, it provides additional features to html. It can also be used with any kind XML document .