$ gem install csscss
$ csscss path/to/styles.css path/to/other-styles.css

{.contact .content .primary} and {article, #comments} share 5 rules
{.profile-picture}, {.screenshot img} and {a.blurb img} share 4 rules
{.work h2:first-child, .archive h2:first-child, .missing h2:first-child, .about h2, .contact h2} and {body.home h2} share 4 rules
{article.blurb:hover} and {article:hover} share 3 rules

挺好使的。好像类似的也有一些。