Google Chrome already allows forcing dark mode for Web Contents via a flag, Chromium team offers another flag in Android version of Chrome Canary to display “Darken websites” checkbox in themes settings to let user apply the dark theme for sites, provided, theme setting should be set to System default or Dark.
Chrome browser respects system theme setting and displays its browser UI accordingly. For instance, if you’ve set device theme to light/dark, Chrome changes its UI related to that. If you now visit chrome://flags page in Canary and turn on the “Darken websites checkbox in the themes Settings” flag, you’ll notice a darken website checkbox under System default or Dark at Chrome themes Settings page: menu > Settings > Themes.
Selecting the checkbox enables dark mode/dark theme for websites in Chrome Canary.
Here is what the flag description says “Show a darken websites checkbox in themes settings when system default or dark is selected. The checkbox can toggle the auto-darkening web contents feature -Android”.
Google is already working to provide a global setting for desktop Chrome on Windows, Mac, Linux and iOS platforms to “allow users to force web content light/dark mode independent of system setting.
Related articles:
Google Chrome adds dark theme to Reader Mode
You can now enable dark mode on all websites in Chrome Canary on desktop
It is possible to Disable dark mode in Chrome only, but not for Windows 10
How to turn off dark mode for Chrome on Windows 10
Chrome Canary now supports dark mode in Windows 10 and respects light/dark mode Setting