For example:
https://drafts.csswg.org/css-backgrounds-3/#border-radius
Notice the "Diagram of the inscribed ellipse" image, not loading. It points to:
https://drafts.csswg.org/css-backgrounds-3/corner.png
Which is 404ing (along with what seems to be most other images on that page).
I've noticed this on a number of different CSS spec pages over the past week.