How to make camera move backwards in relation to player (so behind player), regardless of y rotation of player and camera

So im having trouble doing this, and i need to know how to fix the following code. I want it so that when the mouse moves down, it becomes a top down view gradually (depending on how much the mouse is moved) and that requires rotation of the camera on the x axis, and movement on z and y axis, z axis is the problem.

 using UnityEngine;
 using System.Collections;
 
 public class CameraController : MonoBehaviour {
     
     public float Sensitivity;
     public float MaxDistance;
     public float MaxAngle;
     private float MouseY;
     private float MouseYSet;
     private float CameraAngle;
     private float PlayerHead;
     private float PlayerBack;
     
     public Vector3 CameraDistance;
     private Vector3 BackPos;
     private Vector3 TopPos;
 
     public GameObject CameraTarget;
     
     void Start () {
         PlayerHead = CameraTarget.transform.localPosition.y + CameraTarget.transform.localScale.y / 2;
         PlayerBack = CameraTarget.transform.localPosition.z - CameraTarget.transform.localScale.z / 2;
     }
     
     void Update () {
         // Look controls
         MouseY -= Input.GetAxisRaw ("Mouse Y");
         CameraAngle = Mathf.Clamp (CameraAngle + (MouseY - MouseYSet) * Sensitivity * 10, -MaxAngle, MaxAngle);
         CameraDistance = new Vector3 (CameraTarget.transform.localPosition.x, Mathf.Clamp (CameraDistance.y + (MouseY - MouseYSet) * Sensitivity * 10, CameraTarget.transform.localPosition.y, PlayerHead + MaxDistance), Mathf.Clamp (CameraDistance.z + (MouseY - MouseYSet) * Sensitivity * 10, PlayerBack - MaxDistance, CameraTarget.transform.localPosition.z));
         BackPos = new Vector3 (CameraTarget.transform.localPosition.x, CameraTarget.transform.localPosition.y, PlayerBack - MaxDistance);
         TopPos = new Vector3 (CameraTarget.transform.localPosition.x, PlayerHead + MaxDistance, CameraTarget.transform.localPosition.y);
         if (MouseY != 0)
         {
             transform.localRotation = Quaternion.Euler (CameraAngle, transform.localRotation.y, transform.localRotation.z);
             transform.localPosition = new Vector3 (CameraDistance.x, CameraDistance.y, CameraDistance.z);
             transform.localPosition = Vector3.Slerp (BackPos, TopPos, Sensitivity * 10);
             MouseYSet = MouseY;
         }
     }
 }