Many comments here say that that's what browser says but there is no way to distinguish UI theme from content theme and it's impossible to have dark UI with lig

Many comments here say that that's what browser says but there is no way to distinguish UI theme from content theme and it's impossible to have dark UI with light content due to browser limitation. Hence, as they say, it's a problem of a browser, not a web-site. If it's obvious for everybody that these content negotiation signals from a browser lack crucial information as to distinguishing between UI and content preferences, maybe it's safer to keep standard default (usually light) and just offer and option to switch to dark in case user wants. Hence, my post here to show this situation. There is no need to force dark theme in the absence of enough information from a browser as to user preferences.