How do I tighten or tone the back of my calves?

[M.Horn]

I'm trying to wear shorts this summer because it's been so long since I wore shorts. I have no problem with the size of my thighs and calves. I walk everyday for 40mins and it has gotten my legs slimmer but it's the back of my calves I have an issue with it. They jiggle! I don't think I'm targetting the muscle back there. I'm not trying to get bulky or muscular legs. I'm just trying to get my calves toned, basically toned and lean calves muscle so they don't jiggle. Any help is appreciated, thanks.