Unable to find style in skin repaint

I've found a person with a similar problem here, but I still cannot fix the problem.

In short, Unity fails to recognize my custom GUISkin. I've deleted the skin and started from scratch because I did rename the skin (see problem linked above). Still, I've checked all of these possible problems (I'm using c#):

• The skin exists, it is named BaseSkin

• The GUISkin is a public property of my MonoBehavior (subclass name is PresetButtons, attached to empty game object named GUIPresetButtons). Property is: public GUISkin customSkin;

• The public property customSkin is definitely set via Inspector.

• in OnGUI, I set GUI.skin to customSkin

• NO compilation errors or warnings.

• The exact error is "Unable to find style 'ButtonPreset01' in skin 'GameSkin' Repaint" yet my skin is named BaseSkin.

• 'ButtonPreset01' clearly exists in BaseSkin's Custom Styles (though it appears Unity is looking in the default skin anyway.

I feel like I've tried everything, read the GUISkin documentation thoroughly, and read all the related answers I could find. Here is the GUI.Button call:

  void OnGUI () {
 
  GUI.depth = 0;
 
  GUI.skin = customSkin;
  
  if (GUI.Button(new Rect(0,0,80,80), "", "ButtonPreset01")) {
  Debug.Log("Clicked Preset 1 button");
  }
 
  }

Am I doing this wrong?