// Modifies only the button style of the current GUISkin

var style : GUIStyle;

function OnGUI() {
GUI.skin.button = style;
GUILayout.Button("This is a button.");
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
public GUIStyle style;
void OnGUI() {
GUI.skin.button = style;
GUILayout.Button("This is a button.");
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

public style as GUIStyle

def OnGUI():
GUI.skin.button = style
GUILayout.Button('This is a button.')