error CS0103: The name `String' does not exist in the current context

I need help solving the error that is in the title.

  1. DevLogin.cs(5,35): error CS0103: The name `String’ does not exist in the current context

  2. DevLogin.cs(6,35): error CS0103: The name `String’ does not exist in the current context

    using UnityEngine;
    using System.Collections;

    public class Devlogin : MonoBehaviour {
    private string username = String.Empty;
    private string password = String.Empty;
    private bool correctLogin;

    void  Update (){
    	correctLogin = (username == "LegendWill" && password == "admin");
    }
    
    void  OnGUI (){
    	Rect windowRect;
    	windowRect.x = Screen.width / 2 - 100;
    	windowRect.y = Screen.height / 2 - 50;
    	windowRect.width = 200;
    	windowRect.height = 100;
    	GUI.Window(0, windowRect, OnWindowGUI, "Authentication");
    }
    
    void  OnWindowGUI (){
    	username = GUILayout.TextField(username);
    	password = GUILayout.PasswordField(password, '*'[0]);
    	if (GUILayout.Button("Login") && correctLogin)
    	{
    		Debug.Log("You logged in!");
    		enabled = false;
    	}
    }
    

    }

It’s string.Empty with lowercase s

using UnityEngine;
using System.Collections;

public class Devlogin : MonoBehaviour {
    private string username = string.Empty;
    private string password = string.Empty;
    private bool correctLogin;

    void Update (){
        correctLogin = (username == "LegendWill" && password == "admin");
    }

    void  OnGUI (){
        Rect windowRect = new Rect(Screen.width / 2 - 100, Screen.height / 2 - 50, 200, 100); // You need to instantiate the rect object, constructor takes what you were setting property by property.
        GUI.Window(0, windowRect, OnWindowGUI, "Authentication");
    }

    void  OnWindowGUI (int id){
        username = GUILayout.TextField(username);
        password = GUILayout.PasswordField(password, '*');  // I have no idea what you were doing with [0].
        if (GUILayout.Button("Login") && correctLogin)
        {
            Debug.Log("You logged in!");
            enabled = false;
        }
    }
}