If I can be totally honest, the Plasma theme “Expose Metallic” by kde community contributor ‘phob1an’ is doing a LOT of the heavy lifting here. It themes the window decorations, the task switcher, and the application launcher.

I applied some tweaks with Kvantum Manager to remove transparency in some areas that felt out of place.

The Konsole Frame is just that, the “Konsole Frame” widget from the built in widget store. It adopted the silver window border automatically, which actually surprised me somewhat.

All Qt6 apps should adopt the theming automatically, but ymmv depending on the ecosystem you’ve deployed.