Progressive Enhancement

The Progressive Enhancement is a web design strategy which is the opposite of graceful degradation.

A basic markup document is created, geared towards the lowest common denominator of browser software functionality, and then the designer adds enhancements to the presentation and behaviour of the page, using modern technologies like Cascading Style Sheets or JavaScript.

In other words Progressive enhancement is a strategy for web design that emphasizes accessibility, semantic HTML markup, and external stylesheet and scripting technologies. Progressive enhancement uses web technologies in a layered fashion that allows everyone to access the basic content and functionality of a web page, using any browser or Internet connection, while also providing those with better bandwidth or more advanced browser software an enhanced version of the page.