As a side note, yes I do see #762936 but I'm pretty sure this issue is separate, and this package worked OK for me with GTK 3.18 and earlier.
X -- GPG: ed25519/56034877E1F87C35 GPG: rsa4096/1318EFAC5FBBDBCE git://github.com/infinity0/pubkeys.git
- Bug#824892: gtk3-engines-xfce: needs to be updated for gtk 3.20 Ximin Luo
- Bug#824892: Acknowledgement (gtk3-engines-xfce: needs to be... Ximin Luo
