Make object look at UI Image

Hello! I’ve created canvas with image called “sight”. When player is moving mouse, sight is moving too. I also have a gun on scene, and i want to rotate this gun to make him look at sight. So, how can I transform a rectPosition of sight to worldPosition? Camera.main.ScreenToWorldPoint() just returns a position of camera. Or, maybe, i have to do this task in another way, making a sight out of canvas? Thanks for help

Thanks for answer! I found reason why Camera.main.ScreenToWorldPoint returns a position of camera - you have to add a Z to Input.mousePosition