Does anyone know how they achieved the falling snow effect on this website?

Resident Evil Village website: https://www.residentevil.com/village/us/. From what I've noticed in their code, they added a canvas element over the background image and did something with that. I'm just trying to understand how they managed to put a moving element over an image like that? I can also see that they played around with the element's opacity and z-index, but I still can't understand how they created the snow in the first place. I've tried Googling it, but every animation tutorial that I see only covers the basic transitions and animations, nothing like this.