Not much excitement here really and in fact as much D3 as CSS3.
We create 2 sets of identically positioned circles and from the 2nd set remove some circles we don't want to pulsate. Now we have 2 circles for the data-points we would like to pulsate. Not very pristine as it renders circles we don't need before we remove them, but much easier to read. For a few circles that's fine (I'll apply that to a scatterplot with 20 points to mark outliers), for 500 circles we should use canvas/webGL anyway.
Built with blockbuilder.org