Hi @cactusauvage
funny. I coded belius a long time ago.
I created a couple of images with gradients and move them randomly around on the screen with jQuery.
It is also possible to make the PNG only 1px big and then stretch it super large with CSS. Then it becomes blurry as well and does not get too heavy.
You are welcome to just grab the code I did there.
Also have a look here:
https://jsfiddle.net/mariusjopen/ho2n0nnc/
Best!
Marius