Modernizr provides an easy way to detect any new feature so that you can take the corresponding action. For example, if a browser does not support video feature then you would like to display a simple page.
You can create CSS rules based on the feature availability and these rules would apply automatically on the webpage if the browser does not support a new feature.
You can download the latest version of this utility from Modernizr Download.
Before you start using Modernizr, you would have to include its javascript library in your HTML page header as follows:
<script src = "modernizr.min.js" type = "text/javascript"></script>