This block is a recreation:
I guess the strange flickering effect comes from the definition of a radial gradient: it’s center and width of the radial gradient are defined as a percentage. These percentages are computed among the BBox of the element on which the radial gradient is applied on. Because a cell’s widht/height is constantly evolving (depending on neighbours proximity), the radial gradient’s center/widht is also constantly evolving/shrinking.
See this block for a smoother version.