I needed to detect if Safari was being used as there were some issues with styling on a website I was working upon, only on Mac Safari though!!!
The following code is what I use to detect safari and load the relevant script:
<script type="text/javascript"> if(/Safari/.test(navigator.userAgent)) { //you are using safari, or at least you CLAIM to be document.write('<link type="text/css" media="screen" rel="stylesheet" href="/css/safari.css" title="example" />'); } </script>
Add in the tags and set the path to the correct css file you wish to load. Same concept can be used to load javascript files.