CSS performance 08 Sep, 2010
Some thoughtful and useful reading if you’re at all interested in CSS best practice and performant web site design:
Decorating your markup with classes and ids and matching purely on those while avoiding all uses of sibling, descendant and child selectors will actually make a page perform significantly better in all browsers.Dave Hyatt
To clarify, in his comment Dave is talking about CSS selectors that look like this:
/* Descendant */
ul li {color: #ccc}
/* Child */
p > img {border: .1em solid #ccc}
/* Sibling */
section + section {margin-top: 0}
… and when you think about it, it’s pretty easy to see how these can eat up resource when rendering content in a browser, compared with standard elements. Anyway, check out the post and subsequent discussion: