can confirm it's just a tiled gif :) i recorded it from the game. in the game itself it's texture of a dark noise cloud slowly panning, overlaid on top of a pattern of interweaved lines that changes position constantly.
Yep! It looks a tiled gif. You can also change the tiling style in the css. You can use gifs even though it doesnt say so as backgrounds as long as they fit under 3MB.
