Why does my camera still rotate in the opposite way?

First off I'm a complete newbie and do not know much about Unity or scripting. With that being said I am trying to implement a camera that will rotate on my player on the x axis when i press the a or d key with a being negative and d being positive. The problem arises when I press a say 5 times, the camera will rotate left 5 times which is great. But when I press d 5 times it keeps rotating to the left instead of rotating to the right like I want. I've realized that it's because the rotation angle is still negative. So my thinking of how to fix this would be to reset horizontal in my code to 0 before every time I rotate the angle. This does not work. I'm sure I'm just being a noob and their is an easy fix for this but if anyone could help I'd greatly appreciate it. Thanks.

 using System;
 using UnityEngine;
 
 public class CopiedCamera: MonoBehaviour
 {
     public GameObject target;
     public float rotateSpeed = 5;
     public Vector3 offset;
 
     void start()
     {
     }
 
     void LateUpdate()
     {
         //Possible reason the camera still pans the wrong way is because the angle is still positive or negative
         //When a has been pressed needs to be a negative angle being applied
         //When d has been pressed needs to be a positive angle being applied
 
 
         //float horizontal = Input.GetAxis ("CameraRightLeft") * rotateSpeed;
         float horizontal;
     
         if (Input.GetKeyUp("a"))
         {
             horizontal = 0.0f;
             Debug.Log ("in if");
             horizontal = Input.GetAxis ("CameraRightLeft") * rotateSpeed;
             Debug.Log ("horizontal is: " + horizontal);
             target.transform.Rotate (0, horizontal, 0);
         }
 
         if (Input.GetKeyUp ("d")) 
         {
             horizontal = 0.0f;
             Debug.Log ("in 2if");
             horizontal = Input.GetAxis ("CameraRightLeft") * rotateSpeed;
             Debug.Log ("horizontal is: " + horizontal);
             target.transform.Rotate (0, horizontal, 0);
         }
 
 
         float desiredAngle = target.transform.eulerAngles.y;
         Quaternion rotation = Quaternion.Euler (0, desiredAngle, 0);
         transform.position = target.transform.position - (rotation * offset);
         Debug.Log ("transform position: " + transform.position);
 
         transform.LookAt (target.transform);
     }
 }