A style-less Button for Unity's UIToolkit.

RawButton.cs

using System;
using UnityEngine.Scripting;
using UnityEngine.UIElements;

/** Rather than trying to undo the .unity-button class, we just remove it from
    the element to begin with. */
public class RawButton : Button {
  public RawButton() : this(null) { }

  public RawButton(Action onClick) : base(onClick) {
    this.RemoveFromClassList("unity-button");
  }

  [Preserve]
  public new class UxmlFactory : UxmlFactory<RawButton, UxmlTraits> { }

  [Preserve]
  public new class UxmlTraits : Button.UxmlTraits { }
}