If youre using a Windows system, youll have some Windows hidden secrets in your setup.
It makes the taskbar, Start menu, and some tool menus in dark gray.
The steps to set upNight Lightmode are very simple.

You just need to clickWindows controls > Displayand then selectNight light controls.
To better control the display temperature, see the free appF.lux.
you might achieve your purpose by settingAdjust day and night colors togetherin the menu of F.lux.

Bottom Line
The four methods above are fairly straightforward Windows display tricks to help you focus.