The unity camera rotates with the mouse

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CameraMove : MonoBehaviour {

float _rotationX;
float rotationY;
public float sensitivityHor = 5.0f;
public float sensitivityVert = 5.0f;
public float minimumVert = -45.0f;
public float maximumVert = 45.0f;
// Update is called once per frame
void Update()
{
    // The camera moves 
    //float x = Input.GetAxis("Horizontal") * Time.deltaTime * 5;
    //float y = Input.GetAxis("Vertical") * Time.deltaTime * 5;
    //transform.Translate(x, 0, y);
    // Limit the range of camera movement 
    //float move_x = Mathf.Clamp(transform.position.x, -20f, 20f);
    //float move_y = Mathf.Clamp(transform.position.y, -20f, 20f);
    //float move_z = Mathf.Clamp(transform.position.z, -20f, 20f);
    //transform.position = new Vector3(move_x, move_y, move_z);
    // Click the right mouse button to rotate the camera 
    if (Input.GetMouseButton(1))
    {
        rotationY = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityHor;
        _rotationX -= Input.GetAxis("Mouse Y") * sensitivityVert;
        _rotationX = Mathf.Clamp(_rotationX, minimumVert, maximumVert);
        transform.localEulerAngles = new Vector3(_rotationX, rotationY, 0);
    }

}

}