// Checks if a style name exists

var aStyleName : String = "A Style I have";

function OnGUI() {
    if(GUI.skin.FindStyle(aStyleName) == null) {
        Debug.LogWarning("No style named \"" + aStyleName + "\" could be found");
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public string aStyleName = "A Style I have";
    void OnGUI() {
        if (GUI.skin.FindStyle(aStyleName) == null)
            Debug.LogWarning("No style named \"" + aStyleName + "\" could be found");
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public aStyleName as string = 'A Style I have'

    def OnGUI():
        if GUI.skin.FindStyle(aStyleName) == null:
            Debug.LogWarning((('No style named "' + aStyleName) + '" could be found'))