Better to use
$xf.style.style_id, which will give you the ID of the current style. Using
$xf.visitor.style_id only gives you the preference, which for the vast majority of users (and all guests) will be
0 (which means to use the default style).
Edit: I think it works now. I had to add "$xf.visitor.style_id == 69 OR !$xf.visitor.style_id == 69" for the Dark navigation.
This probably doesn't work the way you expect (or if it does, it's merely incidental). If you wanted to check if the ID was
not 69, you'd use
$xf.style.style_id != 69.