After updating to Fedora 26 from 25, the window title-bars in KDE Plasma 5 were scaled up way beyond what they should be for me.
Took a minute to find out what to do since the option to resize these button is very hidden away. Theme-dependant too!
Navigate: System Settings -> Application Style -> Window Decorations
Click one of the themes context menu icon
Navigate: Window Specific Overrides -> Add
Click "Hide window title bar"
Use . for the regular expression to match all windows*
The original link is: