Pamac-manager window decoration has black bezel

The window of pamac-manager in KDE has a black bezel for a while. Is it a bug or issue in my settings?

I think the issue is in your KDE setting. I have no issue.

Try to check “Setting” → “Appearance” → “Global Theme” → “Application Style” → “Configure GNOME/GTK Application Style…” → Change “GTK theme”

Thank you for the reply!

I checked per your advice. My ‘GTK theme’ is set to ‘Breeze’. I tried to change it to others (Breath, Breath-Dark, Default, and Emacs), the GTK theme changes alright, but the black bezel is still there.

The interesting thing is, this only happens with Pamac-manager, but not any other application window.