The defaul;t styling is done on the a.menu-sibling class
a.menu-sibling {
color:#FFFFFF;
display:inline;
font-family:Verdana,Arial,Helvetica,sans-serif;
font-size:13px;
font-weight:bolder;
text-decoration:none;
}
When you are in a submenu this class doesn't exist.
These settings should be in something like
.menuwrapper a {
color:#FFFFFF;
display:inline;
font-family:Verdana,Arial,Helvetica,sans-serif;
font-size:13px;
font-weight:bolder;
text-decoration:none;
}
For the rest your menu is a very deep nested <font> <font> <font> structure.
I don't know what you did with the show_menus call, but it isn't good formed.
Tip. on my (Dutch) site (
http://websitebaker.allwww.nl/wb/posts/fouten-in-css-oplossen13.php) there are some tools described on how you can debug your css.
Using FF + FireBug it is very simple to see why your CSS didn't work.
Ruud