I can reproduce the issue here on Meta as well on the site that’s on an older commit
I’m pretty sure this is not our bug, I can reproduce it in a fiddle
If you hit run multiple times you’ll notice that the first and second box don’t have the issue.
The first box represents the light theme. it does not have the issue. The second one is one I added a black background to for comparison. It also does not have the issue.
The issue is most noticeable in the third box, which uses the same colors as the default dark theme. I think the color combination is tripping the browser here somehow. I’ve tried all the animation hacks that I’m aware of and the result was still the same.
Short of changing our animation or using different colors, I’m not sure what we can do here other than wait for a fix from the browser, which might not happen any time soon.