Movement Script in C# for Unity

Move.cs

private float speed = 2.0f;
public GameObject character;

void Update () {
		
		if (Input.GetKey(KeyCode.RightArrow)){
			transform.position += Vector3.right * speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.LeftArrow)){
			transform.position += Vector3.left* speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.UpArrow)){
			transform.position += Vector3.forward * speed * Time.deltaTime;
		}
		if (Input.GetKey(KeyCode.DownArrow)){
			transform.position += Vector3.back* speed * Time.deltaTime;
		}
	}

the "vector3" in my visual studio it's not gteen, and it not works. please help!

hover on it and there will be a drop which is showing "using:UnityEngine" or something start with "using" tap on it but make sure you are using the lastest version of the unity.