So I just took the code and I hacked my own together. The reason I worked on it was because I can incorporate my Icon theme's into a stylesheet with linkbranch and I need it if I want to use the workbench tabs where I am working on. Realthunder added some code that it would make it possible to replace the complete tab of the workbench with custom icons.
I also was a bit annoyed about the amount of space was lost by padding in the icons, screenspace I rather use for something usefull.
When I was done I compared it with no stylesheet, and it was pretty much the same. So I kinda just removed the padding on the icons.

I also did some minor tweaks like changing light gray to white on some places and minimizing the fold out icon space. And making the tabs a bit more clear from active to inactive. And the scrollbars are bit darker. Also red outline on the tooltip, which was totally an accident but I kinda like it now.
Below shot from Linkstage with my custom icons: I was thinking about calling it ExtremeProDark so people know it is like ProDark but more EXTREME. Maybe someone can make the lite version the S version and the light version too

I have added the zip file but I have not tested it at all, so use at own risk.