I'm not sure that light text in dark background would improve reading experience... there's a reason why Medium and most news outlets use light background :)
Because habits? Because it's the web's default?
There's also a reason why most developers use dark backgrounds. And why quite some sites are adding dark themes (e.g. YouTube, Twitter).
It's also much nicer when reading with dim lights in the room.
For someone like me who sits in front of 3 monitors for at least 10 hours a day, especially at night, a dark theme is priceless. F.lux does a good job on removing blue colors and therefore relaxing my eyes but its still a huge difference if I have a light or dark background to look at for hours. More and more sites are adding a dark mode these days which makes the ones not having one an annoyance because thats the only window/tab that is bright in an otherwise dark/dimm setup.
You're not sure it would improve your reading experience, that doesn't mean someone else's reading experience wouldn't be improved. It would be a choice, no one would be forced to read white text on dark background. Each with their own preference.
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