4 months late - but I swear, I log in to pump.io like maybe twice a year?  Anyways, I had pretty much given up on installing *any* custom themes in Gnome 3.  Thankfully, emacs, blender, and krita were all things I could configure to have (or already had by default) dark themes and I run them full screen.

My fix for other situations is to bind "xcalib -invert -alter" to super+return (or some other key combination) to invert all colors on the screen.  This is partly because of a longtime frustration with firefox contrasting with dark themes

In a "perfect" world, there would be a gtk3 theme that mimics blender's default theme that I could easily use, and a firefox plugin to allow me to invert a page's contents by default, and de-invert it if I feel like it is necessary for that page.