[Python] How to style GTK grid columns?

[Fabrice Delente <delentef gmail com>]

Hello,

I'm looking for documentation on styling Grid columns, I'd like to
color differently odd and even columns. I have looked at the doc at
gnome.developer.org, about Gtk Style Context and Style Provider, I can
style each cell of the grid with CSS by adding a class to the cell,
but I have spacing between the cells that doesn't get coloured.

Thanks for any hint.