Public Variables not displaying in the inspector

I have some variables in a public class that I want to access in the inpsector. I'm using c# and found out that I have to put in System.Serializable for it to show in the inspector, however it's still not showing. Any thoughts?

 using UnityEngine;
 using System.Collections;
 
 public class CharacterController_2D : MonoBehaviour {
     public float f_speed = 5.0f;
     public SpriteManager[] loopSprites;
     private int in_Direction;
     // Use this for initialization
     void Start () {
         in_Direction = 1;
         for(int i = 0; i < loopSprites.Length; i++)
         {
             loopSprites[i].init();
         }
         Camera.main.transform.position = new Vector3(transform.position.x, transform.position.y, Camera.main.transform.position.z);
     }
     
     // Update is called once per frame
     void Update () {
     if(Input.GetButton("Horizontal"))
         {
             in_Direction = Input.GetAxis("Horizontal") < 0 ? -1 : 1;
             rigidbody.velocity = new Vector3((in_Direction * f_speed),rigidbody.velocity.y,0);
             loopSprites[0].resetFrame();
             loopSprites[1].UpdateAnimation(in_Direction,renderer.material);
         }
         else{
             loopSprites[1].resetFrame();
             loopSprites[0].UpdateAnimation(in_Direction,renderer.material);
         }
     }
     
     public void LateUpdate()
     {
         Camera.main.transform.position = new Vector3(transform.position.x, transform.position.y, Camera.main.transform.position.z);
     }
 }
 
 [System.Serializable]
 public class SpriteManager : MonoBehaviour{
     public Texture2D spriteTexture;
     public int in_framePerSec;
     public int in_gridX;
     public int in_gridY;
     public float f_timePercent;
     private float f_nextTime;
     private float f_gridX;
     private float f_gridY;
     private int in_CurFrame;
     
     public void init(){
         f_timePercent = 1.0f / in_framePerSec;
         f_nextTime = f_timePercent;
         f_gridX = 1.0f/ in_gridX;
         f_gridY = 1.0f / in_gridY;
         in_CurFrame = 1;
     }
     public void UpdateAnimation(int _direction, Material _material){
         _material.mainTexture = spriteTexture;
         if(Time.time > f_nextTime)
         {
             f_nextTime = Time.time + f_timePercent;
             in_CurFrame++;
             if(in_CurFrame > in_framePerSec)
             {
                 in_CurFrame = 1;
             }
         }
         
         _material.mainTextureScale = new Vector2(_direction * f_gridX, f_gridY);
         int in_col = 0;
         if(in_gridY > 1)
         {
             in_col = (int)Mathf.Ceil (in_CurFrame / in_gridX);
         }
         
         if(_direction == 1)
         {
             _material.mainTextureOffset = new Vector2(((in_CurFrame) % in_gridX) * f_gridX, in_col * f_gridY);
         }
         else
         {
             _material.mainTextureOffset = new Vector2(((in_gridX + (in_CurFrame) % in_gridX)) * f_gridX, in_col * f_gridY);
             
         }
     }
     
     public void resetFrame(){
         in_CurFrame = 1;
     }
 }