Keeping aside the browser issue (which is already a quite interesting issue)... The correct scaling double square is already an issue with my eyes:

Mixing black and white dots to produce a grey was a pretty common trick when we did not have enough colors in our computers decades ago. But when I step back to lose the perception of the texture, why do I still see a very different grey than the center-grey with the same overall brightness?

I can't even say which one is brighter/darker (my answer changes when I look with a different mindset).