Hi,
This is some suggestions for the UI, would make it much easier in 4k screens and another common HD screens.
and they are not drastic changes.
The 4k screen has 3840x2160. I suggest subtract 60px to operational system bar (taking off at the bottom and on the sides if the bar is on the side) and divide for 3. Then each screen would be 1260x1400 (including browser bar).
that would make the use more easy in some screens with width 1280px
(not only 1366px screens the same as it is now) -> even on 1366 screens it is not well adapted because the operational system could be a lateral bar with 60px obstructing the scroll