title: how to check if we are in single post and check the category of single post?
body: <p>I want to use different <code>css</code> file for one of my categories post in <code>wordpress</code>, for example I want hook different <code>css</code> files for post of news category.
  How can I do this, I search a lot but find nothing.
  I use f<code>unctions.php</code> and <code>wp_queue_style</code> for adding <code>css</code> files to my theme.</p>