Vertical align needs to be in a table cell.

Although most of the article is satire, vertical align has a lot to do with tables. Centering only works in table-cell elements. Take a look at the code http://howtocenterincss.com/#contentType=text&horizontal=cen...

Or, one of the references mozilla links to there is: http://phrogz.net/css/vertical-align/index.html