The morale of this story is that the KDE Plasma settings can screw up your Xfce and GNOME settings. So if you're using multiple desktop environments on a single system -- like my Fedora 25 laptop, or any other Linux system -- you could be in for some pain.
What I was trying to do is configure a dark theme for KDE Plasma (easy) and also use dark themes when running GTK3 and GTK2 apps on the Plasma desktop.
It looked pretty good in KDE Plasma, but things went pear-shaped in GNOME 3 and Xfce. My fonts were screwed up, Menus were gray type on a gray background, and icons were messed up -- with KDE icons bleeding into Xfce.
And then I had trouble logging in with Plasma at all. Blame the Fedora 25 upgrade (and KDE Plasma in general) for that one.
I first tried using the many Xfce configuration utilities to make it right. That didn't do much. I finally was able to log into Plasma (only after a reboot) and attempt to undo the damage. I was partially successful.
In GNOME 3, I had a lot of success with the GNOME Tweak Tool (which should be preinstalled on every GNOME system). I was able to use the Xfce Adiwata Dark theme to make even my GTK2/GTK+ apps look better in GNOME. The whole dark-themed GNOME experience is pretty much better than ever. So that's a win.
And I finally got Xfce looking right. I'm still having display font issues, but everything is more than good enough, and figuring out how to make dark-themed GNOME look better than ever is a bonus.
My new favorite TV show is @BetterthingsFX http://www.fxnetworks.com/shows/better-things/about
AdamW on Linux and more: I don’t like computers https://www.happyassassin.net/2016/11/04/i-dont-like-computers
Rubyland.news is a new Ruby aggregator http://www.rubyland.news
Tech Beacon: Is object-oriented programming dead? Not by a long shot http://techbeacon.com/object-oriented-programming-dead-not-long-shot
Cybersecurity analyst fixes what's broken in NTP (and there was a LOT to fix) http://boingboing.net/2016/11/29/ntp-the-rebirth-of-ailing-fa.html