I'm using a GTK3 app called Tilix. It's a terminal app.
I have 2 computers with KDE Neon based on Ubuntu 16.04 LTS.
In one of them, Tilix works ok. In the other one, no title bars and no scrollbars are painted. It is like they were transparent.
Investigating a little, I've seen it uses the gtk3 theme called Breeze. No theme customization.
I've tried to compare both computers, and to reinstall Tilix. How can I solve this? I think there must be some theme misconfiguration.