/*
#------------------------------------------------------------------------
# Coffe - #1 2011 template (for Joomla 1.5)
#
# Copyright (C) 2007-2010 Gavick.com. All Rights Reserved.
# License: Copyrighted Commercial Software
# Website: http://www.gavick.com
# Support: support@gavick.com   
#------------------------------------------------------------------------ 
# Based on T3 Framework
#------------------------------------------------------------------------
# Copyright (C) 2004-2009 J.O.O.M Solutions Co., Ltd. All Rights Reserved.
# @license - GNU/GPL, http://www.gnu.org/copyleft/gpl.html
# Author: J.O.O.M Solutions Co., Ltd
# Websites: http://www.joomlart.com - http://www.joomlancers.com
#------------------------------------------------------------------------
*/

/* HERE YOU CAN PUT YOUR OWN CSS RULES */
<style type="text/css"> #flasho{z-index:0;} #boxo{top:200px;left:400px;border:1px double #600;width:532px;height:210px;margin:0px;z-index:100;position:absolute;display:none;background:#FFFFFF;} #transo{background:#000000;height:400px;;width:100%;-moz-opacity:.80;top:0px;left:0px; filter:alpha(opacity=80); opacity:.80;display:none;position:absolute;z-index:99;} </style> <script type="text/javascript"> function addthiseffect() { document.getElementById('transo').style.display="block"; document.getElementById('boxo').style.display="block"; } </script>

Reference: http://rooturaj.com/technology/displaying-html-div-above-flash-content-transparency-z-index/#ixzz1SyLHAbeH