app.css for gtk3
 

I have a SoftMaker office suite. I need to change
the base color for the program so I can use the
GnomishDark gtk3 theme.

Which widget would I use in an app specific .css file
to change the base color of the spreadsheet and word
processor workheets area only ?

I'm sure it only needs about 3 lines of code to do it,
like some I've seen for .mozilla gtkrc workarounds.

Clues ?

THX

Patrick