There is nothing really to say about it; the screenshots are explaining it by themselves. It looks like an active CSS Debugging.
The bug has existing since weeks/months.
iOS 17.5 (I updated today).
Using in browser, Edge version 124.0.2478.89
No matter if I’m logged in or not.
The bug seems to only happening on stackoverflow.com and their subdomains. Because Stack Exchange is looking normal.