It's definitely possible to cause browser failures with pure CSS if you figure out how to stress the renderer. For example, if your set of transforms and animations require the browser to allocate lots of temporary surfaces, it can run out of RAM (or VRAM) and then the tab might get killed to free up resources. This is more likely to happen on mobile, but it can happen on desktop too.

Crashing a browser process with CSS is certainly up there in WTF moments. I've had to debug one such situation in the past: https://news.ycombinator.com/item?id=25265708

The call chain from the renderer can be surprisingly deep.