After a system (as well as KDE) update, I got this blue panel glow which appears on hover.

I browsed through system settings, panel settings, desktop settings, but couldn't find an option to change/remove this blue glow. Did anyone else encounter this problem? Where should I look?
I also tried this, but it didn't help.
I use Arch, but don't think it matters much in this case...
Thank you.

