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);                                
     }
 }