As the universe expands, the density of radiation and ordinary dark matter declines more quickly than the density of dark energy (see equation of state) and, eventually, dark energy dominates. Specifically, when the scale of the universe doubles, the density of matter is reduced by a factor of 8, but the density of dark energy is nearly unchanged (it is exactly constant if the dark energy is the cosmological constant).
as the universe expands the density of radiation and ordinary dark matter declines more quickly than the density of dark energy (see equation of state) and eventually dark energy dominates specifically when the scale of the universe doubles the density of matter is reduced by a factor of 8 but the density of dark energy is nearly unchanged (it is exactly constant if the dark energy is the cosmological constant)