New Feature: Lightbox

Any element in your presentation can now be turned into an image/video lightbox trigger. Clicking reveals a full-size lightbox overlay where users can view your image or video. This is great for things like clickable thumbnails in a gallery.

<!-- Click to show "A.png" in an overlay -->
<img src="A.png" data-preview-image>

<!-- Click show "B.png" in an overlay -->
<img src="A.png" data-preview-image="B.png">

<!-- Click to show "C.mp4" in an overlay and scale it to "cover" -->
<img src="A.png" data-preview-video="C.mp4" data-preview-fit="cover">

<!-- Works with any element type -->
<button data-preview-video="C.mp4">Play video</button>

Docs: revealjs.com/lightbox.

Here's what it looks like in action:

https://github.com/user-attachments/assets/3d7d5885-8099-412c-b26d-ef294adbbb3d

Changes

• Upgrade to gulp 5.0.
• Add controls: "speaker-only" config option for only showing controls in speaker view (@gpotter2 in https://github.com/hakimel/reveal.js/pull/3716)