How do I make my charcter Lean/Tilt in the directon of movement.

Kyberous

I'm currently recreating the scene that was showed in the "how to make a game look good" video however I'm struggling with the part where he implemented a script that leans the rectangle when he moves left or right. I assume he did this through script as to not cause issues with either the box collider and or shadow caster and I want the same effect. everything else like the level design, coin collection and lighting I've figure out but this has me stumped, any help would be appreciated, thanks.