http://cdpn.io/hKlqr – Here’s your Codepen link.
If it isn’t obvious, it will not look that when I’ve finished. This is just a test. The button would, of course, be more obvious and would most likely be in the centre of the screen (horizontally). Additionally, for some reason, when Codepen generates it the image isn’t changing when you hover over it. But, it works on a normal preview.
I didn’t think it was possible either, with the :target pseudo but there’s a whole lot I don’t know yet.
It looks like I’ll have to use JS after all.
Oh, and you’re right about the nav:target … except I meant to use #nav:target which should only target elements with the id of “nav”.