https://arstechnica.com/gadgets/2019/01/chromes-getting-a-dark-mode-on-windows-to-match-the-one-for-macos/

Chrome 73 is going to include support for macOS 10.14's dark mode, with an alternative color scheme for its user interface that cuts the brightness. It's now clear that a Windows version of the same is in development, though it seems to trail the macOS version.

A bug report was spotted by Techdows, and preliminary work has been started to bring Windows its dark mode. Unlike its macOS counterpart, which should track the operating-system mode, the Windows dark mode currently has to be forcibly turned on with a command-line switch. Adding "--force-dark-mode" to the command line of current builds of Chrome 73 makes everything dark.