Based on this method, the sky would have the brightness of a 60W incandescent lamp seen from a distance of 4 km. It would be extremely weak, but not completely jet-black.
Previous approaches relied on ultraviolet light from short-lived giant stars, but these were not as reliable as they might miss the weakest stars. The Blazar approach measures the light of each galaxy, even if they are too small to be detected. And while people had previously measured the background light between the galaxies, they were trying to study the light directly and had to fight the Milky Way's interference.
This is not a very accurate representation, at least not yet. In addition to the remaining 1