There is a hover effect, but it is more subtle than others - I relied on positioning to communicate that they're buttons more than colour and effect; I will need to rethink it.
I do have some fancy designer monitors with accurate colours and when doing web development I do test on normal monitors, but I didn't this time as I just forgot.
Edit: I just tested on my bad monitors and I can see the outlines perfectly fine, faint but clearly visible (on a TN panel it's actually blaringly obvious). I might need to test on another monitor but can you confirm that your contrast settings on your monitor is 0/default and you can't see the outline or tab button hover effects?