Capsule Collider stays on floor when my character jumps

Whenever my character jumps its capsule collider stays on floor while he goes into the air. I am new to all this so can someone explain how to fix this issue and what do i have to change in my script.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Player_Controler : MonoBehaviour
 {
     public bool isGrounded;
     public bool isCrouching;
 
     private float speed;
     private float w_speed = 0.05f;
     private float r_speed = 0.1f;
     private float c_speed = 0.025f;
     public float rotSpeed;
     public float jumpHeight;
     Rigidbody rb;
     Animator anim;
     CapsuleCollider col_size;
     
 
     // Start is called before the first frame update
     void Start() { 
         rb = GetComponent<Rigidbody>();
         anim = GetComponent<Animator>();
         col_size = GetComponent<CapsuleCollider>();
         isGrounded = true;
     }
     
 
     // Update is called once per frame
     void Update() {
       
 
         //Toggle Crouch
         if (Input.GetKeyDown(KeyCode.LeftControl))
         {
             if (isCrouching)
             {
                 isCrouching = false;
                 anim.SetBool("isCrouching", false);
                 col_size.height = 2;
                 col_size.center = new Vector3(0, 1, 0);
             }
             else
             {
                 isCrouching = true;
                 anim.SetBool("isCrouching", true);
                 
                 speed = c_speed;
                 col_size.height = 1;
                 col_size.center = new Vector3(0, 0.5f, 0);
             }
         }
 
         var z = Input.GetAxis("Vertical") * speed;
         var y = Input.GetAxis("Horizontal") * rotSpeed;
 
         transform.Translate(0, 0, z);
         transform.Rotate(0, y, 0);
         
         if (Input.GetKeyDown(KeyCode.Space) && isGrounded == true)
         {
             rb.AddForce(new Vector3(0, 3, 0), ForceMode.Impulse);
             anim.SetTrigger("isJumping");
             anim.SetBool("isCrouching", false);
             isCrouching = false;
             isGrounded = false;
         }
         
         if (isCrouching)
         {
             //Crouching Controls
             if (Input.GetKey (KeyCode.W))
             {
                 anim.SetBool("isWalking", true);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", false);
             }
             else if (Input.GetKey(KeyCode.S))
             {
                 anim.SetBool("isWalking", true);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", false);
             }
             else
             {
                 anim.SetBool("isWalking", false);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", true);
             }
         }
         else if (Input.GetKey(KeyCode.LeftShift))
         {
             speed = r_speed;
             //Running Controls
             if (Input.GetKey(KeyCode.W))
             {
                 anim.SetBool("isWalking", false);
                 anim.SetBool("isIdle", false); 
                 anim.SetBool("isRunning", true);
             }
             else if (Input.GetKey(KeyCode.S))
             {
                 anim.SetBool("isWalking", false);
                 anim.SetBool("isIdle", false);
                 anim.SetBool("isRunning", true);
             }
             else
             {
                 anim.SetBool("isWalking", false);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", true);
             }
         }
         else if (!isCrouching)
         {
             speed = w_speed;
             //Standing Controls
             if (Input.GetKey(KeyCode.W))
             {
                 anim.SetBool("isWalking", true);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", false);
             }else if (Input.GetKey(KeyCode.S))           
             {
                 anim.SetBool("isWalking", true);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", false);
             }else
             {
                 anim.SetBool("isWalking", false);
                 anim.SetBool("isRunning", false);
                 anim.SetBool("isIdle", true); 
             }
         }
 
     }
     void OnCollisionEnter(Collision col)
     {
         if (col.gameObject.tag == ("Ground") && isGrounded == false)
         {
             isGrounded = true;
             
         }
     }
 }