The new fashion of having borderless windows is quite annoying (struggled with that under both MS Win 10 and Ubuntu).
Here’s the solution for Ubuntu (combined from a couple posts on stack overflow)…
First make “~/.config/gtk-3.0/gtk.css” with the following content:
decoration { border: 1px solid gray;background: gray;
}
Second paste this into shell and after that run “reload_gtk_theme”:
function reload_gtk_theme() { theme=$(gsettings get org.gnome.desktop.interface gtk-theme) gsettings set org.gnome.desktop.interface gtk-theme '' sleep 1 gsettings set org.gnome.desktop.interface gtk-theme $theme }