transform.Rotate on Z axis moves the entire object instead of rotating in place

I’m following an old tutorial of brackeys on how to make a game like color switch(link here:How to make a COLOR SWITCH Replica in Unity (Livestream Tutorial) - YouTube), and I’m trying to make a circle that spins in place.
This is what it looks like:

I added the same script used in the tutorial to the parent object, which is this :
using UnityEngine;

public class Rotator : MonoBehaviour
    public float speed = 100f;

    void Update()
        transform.Rotate(0f, 0f, speed * Time.deltaTime);

The problem is, instead of making the circle rotate in place, the circle rotates around the center point of the parent object.
If anyone can tell me what Im doing wrong here it’ll be really appreciated.

P.S for what it’s worth im using Unity verison 2019.1.8f1

Yea, calling transform.rotate will rotate the transform about its local origin. Is there a reason that your parent object’s center is not the center of the 4 circle pieces? If you move your child objects so that their center aligns with the parent transform then your script should work as intended. Generally speaking, unless you are offsetting for a particular reason then you should have your parent transform align with the children transforms.