Adjust Greeter's CSS for Stretch
I did not check if the same happens on Jessie, but on Stretch the Journal says:
(tails-greeter.py:3017): Gtk-WARNING **: Theme parsing error: greeter.css:1:30: The :insensitive pseudo-class is deprecated. Use :disabled instead.
Maybe we can have something that works both on Jessie and Stretch, and is not deprecated?
Parent Task: #8230 (closed)