Limit Y axis rotation of camera

Good afternoon, I have a simple question but I couldn’t find a solution in the forum that could suit to my code without completely modifying it.
I added a Character Controller to my test capsule and I have the camera (myview) as the player’s child.
It’s a first person player camera, the camera’s view follows mouse direction, but I’d like to limit the up/down rotation so not to rotate vertically more than 90 degrees.

All the other topics I’ve found had a different code from mine and I’m not sure on how to proceed.

Here’s my entire source code:

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

public class CharacterMovement : MonoBehaviour {

    public float speed = 2.0f;                        
    public float sensibility = 2.0f;             

    CharacterController player;							

    public GameObject myview;							

    float leftright;									
    float backforward;									

    float Xrotate;										
    float Yrotate;										

	// Use this for initialization
	void Start () {

        player = GetComponent<CharacterController>();		
	// Update is called once per frame
	void Update () {

   leftright = Input.GetAxis("Horizontal")*speed;				
   backforward = Input.GetAxis("Vertical")*speed;

	Xrotate = Input.GetAxis("Mouse X")*sensibility;
	Yrotate = Input.GetAxis("Mouse Y")*sensibility;

	Vector3 movement = new Vector3(backforward, 0, leftright);			
        transform.Rotate(0, Xrotate, 0);									

	myview.transform.Rotate(-Yrotate, 0, 0);

        movement = transform.rotation * movement;							
	player.Move (movement * Time.deltaTime);								

transform.Rotate(Mathf.Clamp(Xrotate, -90, 90),0,0);
This is untested but Mathf.Clamp should clamp the value between a min and a max value.

hope it helps