Right… I had it working at some point, I guess :focus-within has some limitations. (This could be solved by :target-within, if browsers implement it someday)
iOS Safari, the detail view worked for the first image I clicked on, but just gets stuck on the last image you closed out of. You can still scroll to a new image, but it won’t update to a newly clicked one.
Really nice showcase. While I like non-JS solutions, some kind of JavaScript is almost always needed when creating interactive elements to ensure accessibility.
Also not working here on FF/Linux. Tried Chrome and it's pretty nice. One odd thing I noticed: if I click on an image and then click left or right to go forward or back, after mouse down but before mouse up, the picture index shows "35/35" (it shows the correct position once I release the mouse button).
There is a tiny bit of Javascript to close the overlay with Esc, but other than that, it’s only made by (ab)using HTML and CSS.