I saw this tiny insect and I first thought it was an ant because of the body shape. However its legs were really really green, I’m adding photos but it’s hard to see how green they actually were. It also moved like a spider, and not like an ant which I thought was curious. For reference I live in Norway. Sorry about the grainy pics but it’s a screenshot from a film I took. Hope someone can tell me!
Counting the legs (4 on each side, so 8 in total), it must be a spider. According to the compact body shape and the relatively large "head" (prosoma), I guess it must be a jumping spider (Salticidae) (at least in Europe). Several jumping spider species are known to mimic ants, what also fits the ant-like moving.
A quick web search brought me to the genus Heliophanus which resembles the specimen on your photo (black body, white spots on the opisthosoma and bright legs), whereof four species occur in Norway according to Fauna Europaea:
According to the description on the Spinnenforum (only in German), all four of them match the given characteristics. So, a determination on the species level would need a microscopical dissection.
I found this ant mimicking spider. Could it have been a female? The green legs don´t fit and the 4(?) white dots. I don´t have much experience with spiders, but that might just be variation of their phenotypes.
This genus of spiders lives mostly in the tropics, but a few species occur in temperate regions. I didn´t deep dive into that, but if it is not M.formicaria (De Greer, 1778) there might be another palearctic species that matches your find.