...and here's my one-liner fix for Xubuntu 16.04 (Gtk 3):
sudo sed -i.bak -E 's/^(\s+-GtkScrollbar.+has.+stepper)/#&/' /usr/share/themes/Greybird/gtk-3.0/gtk-widgets.css
...and here's my one-liner fix for Xubuntu 16.04 (Gtk 3):
sudo sed -i.bak -E 's/^(\s+ -GtkScrollbar. +has.+stepper) /#&/' /usr/share/ themes/ Greybird/ gtk-3.0/ gtk-widgets. css