Tree views don't show expand arrows

(sorry, not sure what these are actually called)

Tree views, or at least some of them, don't render the arrows (or was it a +/- on w95? i genuinely don't remember lol). You can still click on the empty space to expand/collapse.

See this pic of the Accounts dialog in Evolution: "On This Computer" should be a child of "Address Books", and "CalDAV" "Contacts" and "On This Computer" should be children of "Calendars":


xfce 4.18 and GTK 3.24.38 on Debian 12 bookworm