Hard code freeze break for gnome-themes-standard

[Cosimo Cecchi <cosimoc gnome org>]

Hi everyone,

I'd like to commit the simple patch attached to [1], which fixes a
regression in gnome-terminal's background color with latest GTK+.
Details are explained in the bug report, and the patch is just a CSS
one-liner.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=645709

Thanks,

Cosimo