Some information on DHTML Menus

I found this great site with lots of DHTML menus.
https://www.dynamicdrive.com/dynamicindex1/index.html

I added this one to my site
https://www.dynamicdrive.com/dynamicindex1/switchmenu.htm

my site
https://www.slavelake.org/

What do you think?

The problem I am having is I do not know how to make my site Valid XHTML with the menu

Can I put this in my style.css or is it better to have it in the header

<style type=”text/css”>
.menutitle{
cursor:pointer;
margin-bottom: 5px;
background-color:#ECECFF;
color:#000000;
width:140px;
padding:2px;
text-align:center;
font-weight:bold;
/*/*/border:1px solid #000000;/* */
}

.submenu{
margin-bottom: 0.5em;
}
</style>

Thanks For all your help