When Chrome 74 was released last week it contained the highly anticipated Dark Mode synchronization with Windows 10 color settings. For many, though, when changing the color settings in Windows 10 to Dark, Chrome would not automatically switch to the Dark Mode. This feature was being rolled out to a limited amount of users at first and would be expanded over the coming days to everyone. For those users who upgraded to Chrome 74 and dark mode was still not working, you could force dark mode by adding the –force-dark-mode command line argument.
Source: https://www.bleepingcomputer.com/news/google/google-chrome-74-now-synchronizes-with-windows-10-dark-mode/