well using my crystal ball, i assume you are using plasma5/kf5, right?
If so, open systemsettings5, navigate to application style, Gnome application style GTK and choose for gtk2 theme oxygen-gtk.
That should fix some glitches.
For gtk3 you have to test, trial and error.
greetings hendrikL
ps.: please provide us every-time you have questions, i mean all you help searching people, the out put of "inxi -v2" so we can see what kind of system you are using and you will get an answer much faster.
To guess what you are talking about is no fun.