How do you make a Tps cam with RotateAround around the X and Y axis without rotating on the Z axis?

Hello, so I have been working on a game and have done some research on this topic, but no one seems to know the answer. I am trying to Rotate the camera around the player around the X and Y axis. Here is my code:

 private void Update()
 {
     if (Input.GetMouseButton(1))
     {
         mainCam.transform.RotateAround(body.transform.position, Vector3.up, Input.GetAxis("Mouse X") * 100 * Time.deltaTime);
         mainCam.transform.RotateAround(body.transform.position, body.transform.right, Input.GetAxis("Mouse Y") * 100 * Time.deltaTime);

     }
 }

After running this code the Z axis will eventually also change value. I get why it does this, but donot know how to fix this. If anyone knows please let me know.