I just upgrade to 1.4.9-2.0.0, and now I got a white border below the menu:

I'm using ubuntu 16.04.02, with Numix theme.
Thanks!!!
This issue was reported on Numix theme repository too. Not sure if it's an upstream issue or it requires a patch on terminix side
I'm not seeing the issue here with Numix, I'll wait to see what the Numix folks have to say.

I also tried it with CSD disabled and toolbar hidden which is what I think the OP has configured, I'm still not able to reproduce it.
I am not able to reproduce either. I will try on Gtk-3.22.
@gnunn1 see https://github.com/numixproject/numix-gtk-theme/issues/655#issue-208975154 I have this problem with Ubuntu 16.04. Terminix+Numix is fine on Ubuntu 16.10.
I think the issue is because of this CSS in terminix:
.terminal-titlebar {
border-bottom: 1px solid @borders;
}
Either Numix does not declare a borders color or it is declaring a white one. You can fix it my overriding the style in ~/.config/gtk-3.0/gtk.css as follows:
.terminal-titlebar {
border-color: black;
}
Change black to whatever color works best for you.
Most helpful comment
I think the issue is because of this CSS in terminix:
Either Numix does not declare a
borderscolor or it is declaring a white one. You can fix it my overriding the style in~/.config/gtk-3.0/gtk.cssas follows:Change black to whatever color works best for you.