i get the popup The type or namespace name 'UI' does not exist and The type or namespace name 'Mono

Unity Engine
1

The type or namespace name ‘UI’ does not exist and
The type or namespace name ‘MonoBehavior’ could not be found

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class Bird : MonoBehaviour
{
private void OnMouseDown()
{
GetComponent().color = Color.red;
}
}

2

The type or namespace name ‘UI’ does not exist => humm weird. Where do you have this error, line 3? UI should be automatically at your references.
The type or namespace name ‘MonoBehavior’ could not be found => That’s because you have removed using UnityEngine; (without UI). It contains MonoBehaviour.

3

the error shows up on unity

4

using UnityEngine;

public class Bird : MonoBehavior
{
private void OnMouseDown()
{
GetComponent().color = Color.red;
}
}
that was the code that it supposed to be