Any pointers on where I can find how to do that? Like I said, everything I have found is using JS to make it work.
Here are a couple versions of what your after using pure CSS.
http://www.websitecodetutorials.com/code/photo-galleries/css-lightbox.php (CSS lightbox)
http://www.websitecodetutorials.com/code/css/css-popup-menu.php (pop up menu in current version but can be anything)
And codedrops has a nice CSS lightbox too (nicer than mine damnit lol).
When using target it’s downfall is that it takes over your back button. Focus downfall is it does not work in touch screens like iPad.
Ehm, in the first link I read that for the 3 :focus examples is needed “(JS help for Safari/Chrome)”,
and for the 3 :target examples is needed “(JS help for IE)” (the :target is only IE9+).
I don’t know if it can fit into your system/model, but out of my hobby room came two scriptless alternatives.
Both are tested in Firefox, Chrome, Opera, Safari-Win and IE7 and IE10; I assume the IE’s between will do it too.
A pure css popup solution
A pure html popup solution