gregfielding on "Quick Mobile Conditional Help"

I'm trying to stick the nav at the bottom on mobile devices, but this code isn't working. What do I need to fix?

Thanks!

<?php if ( wp_is_mobile() ) {
<nav id="site-navigation" class="navbar navbar-inverse navbar-fixed-bottom" role="navigation">
}
else:
{
<nav id="site-navigation" class="navbar navbar-inverse navbar-fixed-top" role="navigation">
}
?>