css for button color

[Rudra Banerjee <rudra banerjee aol co uk>]

Dear friends, 
I have a periodic table application written in gtk2
(http://download.savannah.gnu.org/releases/ptbl/).
I wrote it in gtk2 because gnome3.4 with default gtk+ theme Adwaita do
not show colors of button for gtk3 app. Now, from gnome 3.6, this
behavior is applied in gtk2 apps as well.
I discussed this issue previously, with the suggestion that overriding
theme is actually a bad idea, agreed. But for a app like periodic table,
it is basic necessity.
So, I, as suggested before, need to use css for the button colors. Can
anybody kindly help me with creating css? Is gtkcssprovider usable in
gtk2 as well?