How do I get this to Rotate properly?

I have this code here and I was trying to make the rotation be clamped so it can’t rotate all the way around, but now its just rolling up to a certain point. So how do I get it to where it looks up and down and side to side only up to a certain point on each side.

using UnityEngine;
using System.Collections;
using UnityStandardAssets.CrossPlatformInput;

public class CameraRotate : MonoBehaviour

    public float speedH = 2.0f;
    public float speedV = 2.0f;
    private Camera maincamera;
    private float yaw = 0.0f;
    private float pitch = 0.0f;
    private float rotationZ = 0f;
    private float rotationX = 0f;
    void Start()
        maincamera = Camera.main;
    void Update()

        float speed = 10.0f;

        rotationX = CrossPlatformInputManager.GetAxis("Horizontal_2") * speed;
        rotationZ = CrossPlatformInputManager.GetAxis("Vertical_2") * speed;
        rotationX = Mathf.Clamp(rotationX, -90, 90);
        rotationZ = Mathf.Clamp(rotationZ, -90, 90);
        transform.localEulerAngles = new Vector3(rotationX, transform.localEulerAngles.y, rotationZ);

Parent the camera to another gameobject. That gameobject will be your reference to your clamp. Then, simply use Mathf.Clamp to clamp your angle

camera.transform.localEulerAngles = new Vector3(Mathf.Clamp(negativeAngle, positiveAngle), Mathf.Clamp(negativeAngle, positiveAngle), Mathf.Clamp(negativeAngle, positiveAngle));