How can i fix the error code CS0246?

Hello everyone:)

I'm really annoyed with this problem...

Here is the error:

Assets/TypeOut/Scripts/TypeOutEditor.cs(2,7): error CS0246: The type or namespace name UnityEditor' could not be found. Are you missing a using directive or an assembly reference? Assets/TypeOut/Scripts/TypeOutEditor.cs(3,7): error CS0246: The type or namespace name UnityEditorInternal' could not be found. Are you missing a using directive or an assembly reference?

Script:

using UnityEngine;
using UnityEditor;
using UnityEditorInternal; using System;

[CustomEditor(typeof(TypeOutScript))] public class TypeOutEditor : Editor {

 private string ontxt = "Turn On";

 private SerializedObject TOS;
 private SerializedProperty finalText;
 private SerializedProperty On;
 private SerializedProperty Reset;
 private SerializedProperty TotalTypeTime;
 private SerializedProperty TypeRate;
 private SerializedProperty RandomCharacterChangeRate;

 enum TimeModes {TotalTime = 0, TypeRate =1};
 TimeModes TM = TimeModes.TotalTime;
 private float Time = 0.5f;
 private float RCCR = 0.1f;

 public void OnEnable()
 {
     if (target == null)
     {
         return;
     }

     TOS = new SerializedObject(target);
     finalText = TOS.FindProperty("FinalText");
     On = TOS.FindProperty("On");
     Reset = TOS.FindProperty("reset");
     TotalTypeTime = TOS.FindProperty("TotalTypeTime");
     TypeRate = TOS.FindProperty("TypeRate");
     RandomCharacterChangeRate = TOS.FindProperty("RandomCharacterChangeRate");
 }


 public override void OnInspectorGUI() 
 {
     TOS.Update();

     finalText.stringValue = ParseNewline(finalText.stringValue.Trim());

// EditorGUILayout.PropertyField(On); // EditorGUILayout.PropertyField(Reset);

     EditorGUILayout.BeginHorizontal ();

     if(GUILayout.Button(ontxt))
     {
         if (On.boolValue == true)
         {
             On.boolValue = false;
             ontxt = "Turn On";
         }
         else
         {
             On.boolValue = true;
             ontxt = "Turn Off";
         }
     }

     if (On.boolValue == true)
     {
         ontxt = "Turn Off";
     }
     else
     {
         ontxt = "Turn On";
     }

     if(GUILayout.Button("Reset"))
     {
         Reset.boolValue = true;
     }

     EditorGUILayout.EndHorizontal ();

     EditorGUILayout.Space();

// GUI.Label(new Rect(0, 40, 100, 40), GUI.tooltip); EditorGUILayout.LabelField("FinalText:"); EditorGUILayout.LabelField("note: '\\n' for new line"); EditorGUILayout.PropertyField(finalText, GUIContent.none,GUILayout.Height(50));

     EditorGUILayout.Space();

     EditorGUILayout.BeginHorizontal ();

     TM = (TimeModes) EditorGUILayout.EnumPopup(TM);

     if (TM == TimeModes.TotalTime)
     {
         Time = EditorGUILayout.Slider(Time,0f, 10f);
         TotalTypeTime.floatValue = Time;
     }
     else
     {
         Time = EditorGUILayout.Slider(Time,0f, 1f);
         TotalTypeTime.floatValue = -1f;
         TypeRate.floatValue = Time;
     }
     EditorGUILayout.EndHorizontal ();

     EditorGUILayout.Space();

     EditorGUILayout.LabelField("Random Character Change Rate");

     RCCR = EditorGUILayout.Slider(RCCR,0f, 1f);
     RandomCharacterChangeRate.floatValue = RCCR;

     TOS.ApplyModifiedProperties();

 }

 private string ParseNewline(string s)
 {
     s = s.Replace("\\n","|");
     
     string[] SS = s.Split('|');
     
     string ReturnString = "";
     
     foreach (string rp in SS)
     {
         ReturnString = ReturnString + rp + "\n";
     }
     
     return ReturnString;
 }

}

Pls help and describe detailed:)