The answer from @Nambi Narayanan looks very erroneous and poorly implemented. I recommend using the following block:
{block name=head} <link href="/css/mypage.css" rel="stylesheet" type="text/css"/> {/block}
or you can simply add the link tag directly on the page without Smarty:
<link href="/css/mypage.css" rel="stylesheet" type="text/css"/>
source share