How to place button inside window same place

Hi. I made a function called "OptionsWindow" Inside this I have a toolbar on the top. if the toolbarInt is 0 it shows the audio settings, if it's 2, it shows the Graphic settings etc. I have a Back button on each "page" but it's on a different position depending on which toolbarInt is chosen. How can I make the Back button stay on the same position all the time?

This is the code I use for the Back button

 if(GUILayout.Button("Back", GUILayout.Height(buttonHeight)))
             {
                 Debug.Log("Back");
                 audio.PlayOneShot(clickSound);
                 showOptionsWindow = false;
                 showMainMenuWindow = true;
             }

Thanks -Frank