GUI tooltip with background

Is there a simple way to create a GUI.tooltip with background visible only when mouseover a button?
Standard tooltip has no background and its readability depends on what is beneath…

The GUI.tooltip is just a string containing the tooltip message.

It’s up to you to decorate your tooltip display however you wish.
In this simple example, I just went for a Box. You can create your own gui styles to further decorate your tooltip.

function OnGUI () {
    GUI.Button (Rect (10,10,120,20), GUIContent ("Click me", "This is the tooltip"));

    if (!String.IsNullOrEmpty(GUI.tooltip))
        GUI.Box (Rect (10,40,120,40), GUI.tooltip);