[mdarens]

They don't fade away in Chrome because he's using a pseudo-element in the form of content: attr(title). Gecko supports transitions on generated content and WebKit does not.

Also, looking at the ::selection example, it should mentioned that it's not safe to group vendor prefixes in the selector portion of a declaration block, as, unlike with properties, the whole block will be skipped if an unrecognized selector is encountered by a UA's CSS parser.