How do I draw a raycast with my mouse position that is relative to the main camera?

I'm trying to learn raycasting and have the following code.

 Vector3 mousePos = Camera.main.ScreenToViewportPoint(Input.mousePosition);

     Vector2 targetDirection = new Vector2(mousePos.x, mousePos.y);

     RaycastHit2D hit = Physics2D.Raycast(transform.position, targetDirection, rayLength);

     Debug.DrawRay(transform.position, targetDirection, Color.green);

I think the problem is I don't know how to adjust my mousePos variable to be relative to my camera.