Hey Kasey,
I went ahead and created a video tutorial and the following CSS code snippets to show you how to do this.
You can Check Out The Video Tutorial Here:
http://vimeo.com/20892937
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CSS Code To Accompany The Video Tutorial
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This CSS will style ALL of your Custom Menus in the Default Catalyst Styling:
Code:
.widget_nav_menu {
background: #F6F6F6;
border-top: 1px solid #E8E8E8;
border-bottom: 1px solid #E8E8E8;
height: 32px;
margin: 0 auto;
padding: 0;
color: #333333 !important;
font-size: 12px;
line-height: 1em;
float: none;
}
.widget_nav_menu ul {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
.widget_nav_menu li {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
.widget_nav_menu li a, .widget_nav_menu li a:link, .widget_nav_menu li a:visited {
background: #F6F6F6;
border-right: 1px solid #E8E8E8;
margin: 0;
padding: 10px 15px;
color: #333333 !important;
text-decoration: none !important;
display: block;
}
.widget_nav_menu li a:hover, .widget_nav_menu li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
.widget_nav_menu li li a, .widget_nav_menu li li a:link, .widget_nav_menu li li a:visited {
background: #F6F6F6;
width: 150px;
border-top: 0 solid #E8E8E8;
border-right: 1px solid #E8E8E8;
border-bottom: 1px solid #E8E8E8;
border-left: 1px solid #E8E8E8;
margin: 0;
padding: 10px 10px;
color: #333333 !important;
text-decoration: none !important;
float: none;
}
.widget_nav_menu li li a:hover, .widget_nav_menu li li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
.widget_nav_menu ul li {
margin: 0;
padding: 0;
list-style: none;
}
.widget_nav_menu li ul {
width: 150px;
height: auto;
margin: 0;
padding: 0;
z-index: 9999;
left: -999em;
position: absolute;
}
.widget_nav_menu li ul ul {
margin: -33px 0 0 171px;
}
.widget_nav_menu li:hover ul ul, .widget_nav_menu li:hover ul ul ul {
left: -999em;
}
.widget_nav_menu li:hover ul, .widget_nav_menu li li:hover ul, .widget_nav_menu li li li:hover ul {
left: auto;
}
.widget_nav_menu li.current-menu-item a {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
This CSS is the same as above, but with no values so you can add your own custom styling if you want to start with a clean slate:
Code:
.widget_nav_menu {
}
.widget_nav_menu ul {
}
.widget_nav_menu li {
}
.widget_nav_menu li a, .widget_nav_menu li a:link, .widget_nav_menu li a:visited {
}
.widget_nav_menu li a:hover, .widget_nav_menu li a:active {
}
.widget_nav_menu li li a, .widget_nav_menu li li a:link, .widget_nav_menu li li a:visited {
}
.widget_nav_menu li li a:hover, .widget_nav_menu li li a:active {
}
.widget_nav_menu ul li {
}
.widget_nav_menu li ul {
}
.widget_nav_menu li ul ul {
}
.widget_nav_menu li:hover ul ul, .widget_nav_menu li:hover ul ul ul {
}
.widget_nav_menu li:hover ul, .widget_nav_menu li li:hover ul, .widget_nav_menu li li li:hover ul {
}
.widget_nav_menu li.current-menu-item a {
}
This CSS is what you will want to use if you need to focus your styling on a specific Custom Menu. As you can see with this particular example, this will style a Custom Menu with an ID of #nav_menu-1. The 1 is the ID, so just change this to the Custom Menu ID that you're working on and it should style ONLY that Custom Menu. You can use Firebug to determine the actual number:
Code:
#nav_menu-1 {
background: #F6F6F6;
border-top: 1px solid #E8E8E8;
border-bottom: 1px solid #E8E8E8;
height: 32px;
margin: 0 auto;
padding: 0;
color: #333333 !important;
font-size: 12px;
line-height: 1em;
float: none;
}
#nav_menu-1 ul {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
#nav_menu-1 li {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
#nav_menu-1 li a, #nav_menu-1 li a:link, #nav_menu-1 li a:visited {
background: #F6F6F6;
border-right: 1px solid #E8E8E8;
margin: 0;
padding: 10px 15px;
color: #333333 !important;
text-decoration: none !important;
display: block;
}
#nav_menu-1 li a:hover, #nav_menu-1 li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
#nav_menu-1 li li a, #nav_menu-1 li li a:link, #nav_menu-1 li li a:visited {
background: #F6F6F6;
width: 150px;
border-top: 0 solid #E8E8E8;
border-right: 1px solid #E8E8E8;
border-bottom: 1px solid #E8E8E8;
border-left: 1px solid #E8E8E8;
margin: 0;
padding: 10px 10px;
color: #333333 !important;
text-decoration: none !important;
float: none;
}
#nav_menu-1 li li a:hover, #nav_menu-1 li li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
#nav_menu-1 ul li {
margin: 0;
padding: 0;
list-style: none;
}
#nav_menu-1 li ul {
width: 150px;
height: auto;
margin: 0;
padding: 0;
z-index: 9999;
left: -999em;
position: absolute;
}
#nav_menu-1 li ul ul {
margin: -33px 0 0 171px;
}
#nav_menu-1 li:hover ul ul, #nav_menu-1 li:hover ul ul ul {
left: -999em;
}
#nav_menu-1 li:hover ul, #nav_menu-1 li li:hover ul, #nav_menu-1 li li li:hover ul {
left: auto;
}
#nav_menu-1 li.current-menu-item a {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
And here is a "clean slate" version of the ID specific CSS:
Code:
#nav_menu-1 {
}
#nav_menu-1 ul {
}
#nav_menu-1 li {
}
#nav_menu-1 li a, #nav_menu-1 li a:link, #nav_menu-1 li a:visited {
}
#nav_menu-1 li a:hover, #nav_menu-1 li a:active {
}
#nav_menu-1 li li a, #nav_menu-1 li li a:link, #nav_menu-1 li li a:visited {
}
#nav_menu-1 li li a:hover, #nav_menu-1 li li a:active {
}
#nav_menu-1 ul li {
}
#nav_menu-1 li ul {
}
#nav_menu-1 li ul ul {
}
#nav_menu-1 li:hover ul ul, #nav_menu-1 li:hover ul ul ul {
}
#nav_menu-1 li:hover ul, #nav_menu-1 li li:hover ul, #nav_menu-1 li li li:hover ul {
}
#nav_menu-1 li.current-menu-item a {
}
**UPDATE**
With the above CSS your Custom Navbar may not fill the entire width of the area you add it to.
If this is the case you can just add a Width to it by either doing a width: 100%; or a width: 960px (or whatever the width of that area is).
You would add this Width style to either the .widget_nav_menu class or the #nav_menu-1 ID like so:
Code:
.widget_nav_menu {
width: 100%;
}
or
Code:
#nav_menu-1 {
width: 100%;
}
**UPDATE #2**
The following CSS should give you a solid starting point for styling a WP Custom Menu Widget when added to a Widget Area in Appearance > Widgets.
This particular snippet of CSS is specifically suited for a stock 280px width Sidebar 1, so if you add it to a widget area with a different width then you'll need to adjust accordingly. Also note that this will style ALL of your Custom Menu Widgets so if you only want to style a particular one you'll have to specify the specific Custom Menu ID as mentioned above.
Code:
.widget_nav_menu {
background: #F6F6F6;
border-top: 1px solid #E8E8E8;
border-bottom: 1px solid #E8E8E8;
height: 32px;
margin: 0 auto;
padding: 0;
color: #333333 !important;
font-size: 12px;
line-height: 1em;
float: none;
}
.widget_nav_menu ul {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
.widget_nav_menu li {
margin: 0;
padding: 0;
float: left;
list-style: none;
}
.widget_nav_menu li a, .widget_nav_menu li a:link, .widget_nav_menu li a:visited {
background: #F6F6F6;
border-bottom: 1px solid #E8E8E8;
margin: 0;
padding: 10px 15px;
color: #333333 !important;
text-decoration: none !important;
display: block;
}
.widget_nav_menu li a:hover, .widget_nav_menu li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
.widget_nav_menu li li a, .widget_nav_menu li li a:link, .widget_nav_menu li li a:visited {
background: #F6F6F6;
width: 230px;
border-top: 0px solid #E8E8E8;
border-right: 0px solid #E8E8E8;
border-bottom: 0px solid #E8E8E8;
border-left: 0px solid #E8E8E8;
margin: 0;
padding: 10px 25px;
color: #333333 !important;
text-decoration: none !important;
float: none;
}
.widget_nav_menu li li a:hover, .widget_nav_menu li li a:active {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
#sidebar-1 .widget_nav_menu ul, #sidebar-2 .widget_nav_menu ul, #ez-home-sidebar-1 .widget_nav_menu ul {
border-top: 1px solid #E8E8E8;
padding: 0;
}
#sidebar-1 .widget_nav_menu ul li, #sidebar-2 .widget_nav_menu ul li, #ez-home-sidebar-1 .widget_nav_menu ul li {
width: 280px;
margin: 0;
padding: 0;
list-style: none;
clear: both;
}
#sidebar-1 .widget_nav_menu ul ul, #sidebar-2 .widget_nav_menu ul ul, #ez-home-sidebar-1 .widget_nav_menu ul ul {
border-top: 0;
margin-top: -1px;
padding: 0;
}
.widget_nav_menu li ul {
border-bottom: 1px solid #E8E8E8;
width: 280px;
height: auto;
margin: 0;
padding: 0;
z-index: 9999;
left: -999em;
position: absolute;
}
.widget_nav_menu li ul ul {
margin: -33px 0 0 171px;
}
.widget_nav_menu li:hover ul ul, .widget_nav_menu li:hover ul ul ul {
left: -999em;
}
.widget_nav_menu li:hover ul, .widget_nav_menu li li:hover ul, .widget_nav_menu li li li:hover ul {
left: auto;
}
.widget_nav_menu li.current-menu-item a {
background: #FFFFFF;
color: #333333 !important;
text-decoration: none !important;
}
Enjoy! 
Eric