Modernizr

"Modernizr is a small and simple JavaScript library that helps you take advantage of emerging web technologies (CSS3, HTML 5) while still maintaining a fine level of control over older browsers that may not yet support these new technologies. Modernizr uses feature detection to test the current browser against upcoming features like rgba(), border-radius, CSS Transitions and many more. These are currently being implemented across browsers and with Modernizr you can start using them right now, with an easy way to control the fallbacks for browsers that don’t yet support them."