CSS Lightbox with Alt Text Viewer

Rather I show you than tell you? Here’s a demo page.

Right now, my blog uses a CSS-based approach using anchors and the <dialog> element to make “lightbox” images work, but I plan to replace this soon with a similar approach that uses the <details> and <summary> elements to provide a more semantically-sound and accessible approach¹.

An additional thing I wanted to implement – again, for the next version of my blog’s theme – was an “alt text viewer”. Mastodon has one, and it’s excellent². Mastodon’s viewer requires JavaScript, but I was inspired when I saw James come up with a CSS-based version that used a re-styled checkbox.

But I wanted to do one better. Displaying alt text, too, seems like an example of what would semantically be best-represented by a <details>/<summary> pair.

My first attempt tried to put the alt-text widget inside the <summary> of the original image, but that’s an accessibility no-no, so instead I wrap both <details> blocks (the lightbox, and the alt-text revealer) inside a container and then reposition the latter over the former. The rest is all the same kinds of tricks I demonstrated previously, to ensure that you can click in-and-out of both in an intuitive way and that keyboard navigation works as you’d expect.

I can’t use it on my blog yet (because if I do, it’ll probably break horribly when I add the functionality to my entire theme, later!), but I’ve put together a demonstration page that showcases the technique, plus a GitHub repo with all of the code (which is all public domain/unlicensed). Go have a play and tell me what you think!