html5 new elements (header, nav, footer, ..) not working in IE
You need to include the HTML5 shiv script in order to allow styling of HTML5 elements in older IE browsers: http://code.google.com/p/html5shiv/
To use, include the following script in your element above your CSS:
<!--[if lt IE 9]>
<script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv.min.js"></script>
<![endif]-->