But when I think about it, this little script can become a nice tool helping to refine the stylesheets of a site.
Maybe as a greasemonkey script, a bookmarklet or a firebug extension.

The only problem that I see is that some of the styles can be dynamical (e.i. :hover). And while it’s not hard to identify “:hover” and “:active” selectors – it’s hard (or impossible?) to predict which styles are user-triggered.

Anyway… just some thoughts at the end of the work week

$A(document.styleSheets).pluck(‘cssRules’).map($A).flatten().pluck(‘selectorText’).each(function(s){
if ($$(s).length === 0) console.log(s);
});

It will work on a jQuery powered sites with a little modification:

if ($(s)[0] === 0) console.log(s);

And using the jQuery $.each function it can be even shorter:

$.each( document.styleSheets, function(i, s) {
$.each( s.cssRules, function (si, ss) {
if (!$(ss.selectorText)[0]) console.log ( ss.selectorText );
});
});

Neat