SUMMARY Kid3 is needing a dark mode for MacOS. When I'm editing songs at night, my eyes hurts from the light mode when all of my other applications are in dark mode, I think this would be a nice addition. SOFTWARE/OS VERSIONS macOS: 10.15.7
Dark mode requires macOS Mojave 10.14.2 or later. Applications which shall support dark mode must be compiled with a recent SDK. Kid3 uses the Qt framework, which would also have to be at least version 5.15 to support dark mode. Unfortunately, for my Mac Mini Apple provides only updates until macOS 10.13 (High Sierra), so I am not able to build such a version or test it. A solution which has been reported to support the dark mode is to use a nightly build from the KDE build factory, which is built with a recent SDK and a patched version of Qt 5.15.2. You can get this version from the "Last Successful Artifacts" section at the top of https://binary-factory.kde.org/job/Kid3_Nightly_macos/.
The alternative would be to use a platform theme plugin (aka integration plugin) like mine (github:RJVB/osx-integration) that will give the same control over style, colour palette, fonts etc. as also exists on other Unix platforms. OR, just add a palette (theme) switcher menu (I think digiKam has one) though you may need the integration plugin for full palette support (can't remember). Personally I just turn down my monitor's luminosity (using an extension for my external which doesn't have hardware buttons for that) and keep enough light in my study to prevent myself from falling asleep...
Fixed in version 3.9.0.