There was an earlier way to install a different Theme for Gramps that allowed to have different colors, sizes of icons etc. Then PaulC created the Themes addon that made the process even easier.
I have tried out various themes downloaded from Gnome-look.org . None of the themes were ever better than the Adwaita used by Gramps as its default.
But I have had a pet peeve with Adwaita in the size of the Tabs.
I found the Windows XP Embedded theme met my Tabs needs but found the theme garish. So I started tweaking and modified it to the Theme I posted to my Github above. It looks great (in my opinion) but has a major flaw that I cannot find. The flaw is hovering over non-active people in the Relationships view and I cannot find where that is being controlled. Hence my initial post.
I have started on another track taking Adwaita Dark Green - Gnome-look.org and stripping it down to the basic Adwaita and now trying to tweak the css files to shrink the tabs. It has the advantage of properly dealing with the hover issue but I do not know how although I do know it does it through scss files.
Maybe when I have nothing else to do (ha ha) or we get our first snow storm I will devote more time to the issue.