IBus GTK3 interface has wrong theming with Breeze GTK theme (GTK+ 3.20), in the screenshot attached below, highlighting of avilable candidates is black, rendering the text unreadable. Reproducible: Always
Created attachment 99779 [details] Black highlighting, not good.
I can confirm that the issue persists with the latest KDE Plasma 5.8.4 on Fedora 25.
An identical problem was fixed in Oxygen-GTK3 a while back - see #329513.
Clickable link: https://bugs.kde.org/show_bug.cgi?id=329513
Seems to be fixed as of master (commit c47a15bce97e3874ca797582f3900d79a9671171) in the Breeze GTK repository.