Hide Pinned Tab Border

Removes the colored border around the selected pinned tab. The tab keeps its tint, so you can still tell which one is selected.

Tabs in the sidebar	Tabs at the top

Turn it on

Open Dia → Settings → Patches and switch on Hide Pinned Tab Border. Or run:

diatweaks enable hidePinnedTabBorder

FAQ

Does it work with tabs at the top?

Yes.