Add Border To Ubuntu Terminal Window

Create ~/.config/gtk-3.0/gtk.css

to contain

/* Decorations */
UnityDecoration {
    -UnityDecoration-extents: 28px 1px 1px 1px;
}

Ref:
https://askubuntu.com/questions/448204/how-do-i-add-a-border-around-windows-but-keep-the-current-theme