Is there a free, preferably open source, reader web app with dark mode? I have an old Lumia lying around which is mostly useless by now but has a nice low-brigh

Is there a free, preferably open source, reader web app with dark mode? I have an old Lumia lying around which is mostly useless by now but has a nice low-brightness screen. BTW, other ideas are welcomed. Hate abandoning perfectly functional tech.