Opera has had limited support for
:focus styling, since (I believe) they wanted to make sure pages were usable and accessible for keyboard users. (Just look at the number of threads on this very forum asking how to remove the 'annoying' outline on links with focus.)
With recent versions Opera has begun to allow more and more styling of focused links – including, unfortunately, removal of the outline.
So Opera 10.50 (or perhaps even 10.00?) and newer let you use this technique for users who navigate with A/Q or Ctrl+Up/Down Arrow. Normal spatial navigation (Shift+arrow key), which is what I assume most Opera keyboard users would use, only navigates to visible elements, though.