UnityEngine.UI is not showing up?

I have a script that needs to access Image.fillAmount but this is only in UnityEngine.UI which doesn't work even though I have Unity UI package installed. Here is my code: using System.Collections; using System.Collections.Generic; using UnityEngine; using TMPro; using UnityEngine.UI;

 public class BattleHud : MonoBehaviour
 {
     public TextMeshProUGUI unitName;
     public TextMeshProUGUI level;
     public Image healthBar;
     
     void Awake()
     {
 
     }
     public void SetHUD(Unit unit)
     {
         unitName.text = unit.unitName;
         level.text = "Lvl. "+unit.level.ToString();
         healthBar.fillAmount = unit.curHealth/unit.maxHealth;
     }
     public void SetHP(Unit unit)
     {
         healthBar.fillAmount = unit.curHealth/unit.maxHealth;
     }
 }