Created attachment 7825 Before (left) and after (right) upgrading. When using Thunar 1.8.1.11 and selecting any Xfce* gtk2 theme, Thunar does neither change its background nor the select color. The title bar changes though. Reproduction: 1. Open Appearance from the settings menu 2. Choose any style in the form of Xfce* (e.g. Xfce-dusk). 3. Open Thunar. Expected result: Thunar's background is black (when choosing Xfce-dusk. May vary when choosing other themes). Actual result: Thunar's background is white (no matter which theme you choose). It looks like the Adwaita theme. I have appended two screenshots which also show the output of screenfetch and the installed versions of Thunar. My display manager is lightdm. OS: Arch Linux Kernel: 4.16.9-1-ARCH Working Thunar version: 1.6.15-1 Non-working Thunar version: 1.8.1.11.gf5147445-1 Only difference is the version of Thunar. Downloaded and installed using pacman. If you happen to have further questions, I'd be glad to answer them.
It's simply because Thunar 1.8.0+ is gtk3-based, therefore you need to use a gtk3-compatible theme. Unfortunately Xfce themes (gtk-xfce-engine) were dropped, so they won't support gtk3 apps, probably distributions will remove them at some point. I strongly suggest you to migrate to a well maintained gtk3 theme such as Adwaita or Greybird. If you really want to stick to a gtk2 theme, you can workaround this by enforcing Thunar (or any other gtk3 app) to use a different theme as described in https://askubuntu.com/a/485662/452351.