Rotate gameObject if cursor is near screen edges

Hi, My game is FPS and I'm trying to rotate a player's gameobject on horizontal and(or) vertical axes (like in "Operation Flashpoint" game). Also, I need to restrict player's rotation. Thing is when I use transform.localEulerAngles = new Vector3(x,y,z); player rotates immidiately, not smooth but rotation restriction is working. But if I use transform.RotateAround(position, axis, angle); player rotates smoothly(perfect!) but no restriction is on. Could you please review my code and tell me what is wrong? Thank you!

 protected void processMove(Vector3 delta)
     {
         crosshairPosition = new Rect(delta.x - crosshairTexture.width/2, Screen.height - (delta.y + crosshairTexture.height/2), crosshairTexture.width, crosshairTexture.height);
         var crosshairPositionVector = new Vector3(crosshairPosition.x, crosshairPosition.y);
 
         cameraX += delta.y * -1 * Time.deltaTime * 0.5f;
         cameraY += delta.x * Time.deltaTime * 0.5f;
 
         Debug.Log(cameraY + " is cameraY");
 
         cameraX = Mathf.Clamp(cameraX, -20, 20);
         cameraY = Mathf.Clamp(cameraY, -20, 20);
 
         if(delta.x >= 630f)
         {
             //Debug.Log("Right SIDE");
             transform.localEulerAngles = new Vector3(transform.localEulerAngles.x, cameraY % 180, 0);
             //transform.RotateAround(transform.position, transform.up, cameraY % 180);
         }
         else if (delta.x <= 90f)
         {
             //Debug.Log("Left SIDE");
             transform.localEulerAngles = new Vector3(transform.localEulerAngles.x, -cameraY % 180, 0);
         }
         else if (delta.y >= 450f)
         {
             //Debug.Log("Upper SIDE");
             transform.localEulerAngles = new Vector3(cameraX % 180, transform.localEulerAngles.y, 0);
         }
         else if (delta.y <= 65f)
         {
             //Debug.Log("Lower SIDE");
             transform.localEulerAngles = new Vector3(-cameraX % 180, transform.localEulerAngles.y, 0);
         }
         else
         {
             //Debug.Log("NOTHING");
         }
     }