Yes, this forces all websites into dark mode, regardless of whether they support it. Based on your title, I assumed that's what you wanted.

Very few websites have already extended their stylesheets for dark mode. If you want more control, I would also recommend a browser that supports extensions (I use Firefox).

It works with flags, just like on desktop. Go to chrome://flags in your address bar and search for "dark". You'll find "Auto dark mode...". Enable it, restart chrome. Done.