Javascript popup

<div id="modal" style="border:3px solid black; background-color:#9999ff; padding:25px; font-size:150%; text-align:center; display:none;">
 This is a modal popup!<br><br>
 <input type="button" value="OK" onClick="Popup.hide('modal')">
</div>

<a href="#" onclick="Popup.showModal('modal');return false;">Show Modal Popup</a>
<br>
<a href="#" onclick="Popup.showModal('modal',null,null,{'screenColor':'#99ff99','screenOpacity':.6});return false;">Show Modal Popup With A Custom Screen</a>