[GNC] No Red negative numbers with gtk-theme enabled

[AC]

As part of trying to get a dark theme for Gnucash I enabled GTK's dark 
theme:

gtk-application-prefer-dark-theme=true

But with that enabled negative numbers no longer show up in red, they're 
all in white.  I don't have any customized CSS that selects for a font 
color so it shouldn't be that.

Is this a CSS accessible property or a direct code-driven property?  If 
it's code driven why is it not overriding the theme?

Where did the GTK themes get stashed on Windows?  I can't find a theme 
anywhere in APPDATA (Local or Roaming), and nothing obvious in Program 
Files (x86).