table{background:black;position:absolute;}
a{color:black;text-decoration:none;font:bold}
td.menu{background:lightgreen}
table.topnav{font-size:80%;top:0;left:0}
table.menu{font-size:100%;bottom:0;z-index:-1}
<script type="text/javascript">
function show_hide_menu()
intShow=setInterval("show()",10)
intHide=setInterval("hide()",10)
document.all("menu").style.bottom=i
document.all("menu").style.bottom=i