A very weird issue has just started in Safari (v14.0.3 on Big Sur 11.2.1).
The scroll bars start shaking and flickering like mad, and the puzzle shakes too.
This appear to affect all kinds of puzzle.
I haven't installed anything or updated Safari or my system when this started. I was using the same Safari session just fine, then a puzzle I clicked starting doing this, and now every puzzle does.
I have tried restarting Safari, rebooting my laptop and emptying the cache on Safari and restarting.
I have recorded a screencapture of the problem at this link: https://imgur.com/gallery/DGq6s13
Many thanks in advance if you are able to suggest anything to fix it.