Customise Supermium on New tab to choose dark mode instead of device theme doesn't work. It will always revert to device theme. Github and Youtube are still in their light mode.

Supermium's dark mode has to be set via a cmdline switch (--force-dark-mode or --enable-features=ForceDarkModeFlag) or by going to chrome://flags/#force-dark-mode, selecting Enabled, followed by a browser restart - then, all sites that also provide a "dark scheme" will preferentially use that; on some sites though, one has to manually select their "dark theme" (user selection stored in a cookie usually...); depends on how the site has been configured...

Disclaimer: My current WinOS doesn't come with a dark "device theme" (isn't that Win10 only?) ...

@Vangelis66 This worked. Thank you.