Hi,
Go to skins/Skin_#/style.css. Open Style.css and find the CSS code below: 
Code:
/* COMPONENT ART HORIZONTAL MENU */
.TopMenuGroup
{
border: solid 0px #000;
background-color: transparent;
line-height:35px;
}
.MenuGroup
{
border: solid 0px #000;
color: #000000;
font-size: 0.8em!important;
margin: 0;
background: #F8F8F8 none;
}
.MenuGroup td, .MenuGroupHover td, .MenuItemHover td, td.MenuItemHover
{
color: #4776BD;
}
.TopMenuItem, .TopMenuItemHover
{
color: #fff;
font-weight: bold;
font-size: 14px;
cursor: hand;
cursor: pointer;
margin:0;
padding: 0 1em!important;
line-height: 35px;
vertical-align:middle;
background: url(images/tab-sep.gif) no-repeat top left;
}
.TopMenuItem
{
background: url(images/tab-sep.gif) no-repeat top left;
}
/*leaf menu items*/
.MenuItem, .MenuItemHover, .MenuItem td, .MenuItemHover td
{
color: #4776BD;
border: solid 0px white;
cursor: hand;
cursor: pointer;
margin: 0;
background: #F8F8F8 none;
width: 100%!important;
}
.MenuItemHover, .MenuItemHover td
{
background: #DCDFE2 none;
}
.ScrollItem
{
background-color: green;
font-size: 0.8em;
border: solid 0px gray;
cursor: default;
text-align: center;
}
.ScrollItemH
{
background-color: aqua;
color: orange;
font-size: 0.8em;
border: solid 0px gray;
cursor: default;
text-align: center;
}
.ScrollItemA
{
background-color: Lime;
color: yellow;
font-size: 0.8em;
border: solid 0px gray;
cursor: default;
text-align: center;
}
The CSSCLASS ".TopMenuItem, .TopMenuItemHover" for the MENU.
The CSSCLASS ".MenuItem, .MenuItemHover, .MenuItem td, .MenuItemHover td" for the submenu.
Thanks