If you would like to add support for HTML5 and CSS3 in old web browsers, we suggest the following lightweight jQuery libraries.
Modernizr is a JavaScript feature-detection library that enables the detection of new HTML5 and CSS3 features such as geolocation and local storage, among others. Also included with Modernizr by default is HTML5 Shiv, a jQuery-based HTML5 polyfill that adds support for the new HTML5 elements in deprecated web browsers.
Concise is built from the ground up to work on mobile devices and that means making use of CSS3's media queries. To help support older browsers that do not support media queries, Respond.js was my polyfill of choice. Respond.js targets browsers from IE 6-8 and is extremely fast and lightweight.