How do I create a sky box?

I’m playing with the 3D features and I can’t figure out if there’s a way to create a sky box effect.

I’d be happy to even just have a static image displayed behind everything, I just don’t know how to do it. Like a parallax layer.

I haven't played too much with 3D yet but for a static image, can you not just set the layer rendering mode to 2D? And maybe parallax to 0,0 so it doesn't move.

And for an actual skybox, can't you just use the default cubes with your sky texture?

Thank you WackyToaster!

I created a layer under everything else and set it to 2D with a parallax of 0,0. I completely forgot to set it to 2D, that was what I was missing.