I was looking at the wiki and only found Linux oriented docs. But it looks like the Tool to use is GTK+ Inspector. Which appears to be enabled via DConf Editor. Unfortunately, the instructions for the DConf Editor are old and written for Linux.
Maybe one of our users whose equally conversant in Linux and Windoze can translate that dialect of Geek Speak?
Then the final step is probably locating the CSS themes used by the actual Gramps main GUI. (Since there seem to be several CSS locations.)
- Howto: Change the Gramps settings via Gnome (accessing DConf Editor)
- GTK+ Inspector
- location of the Gramps Themes