Created attachment 111294 [details] chrome maximized See attachment, Chrome version: 65
Created attachment 111295 [details] chrome unmaximized
This happened after plasma 5.12.2 > 5.12.3 update, on 5.12.2 buttons fit just perfect
This bug doesn't exist in current versions of Chromium and Breeze GTK, so I'm closing this. Backporting the existing fix is under consideration in the meantime.