How to add space between menu and dropdown submenu

Question

I'm working on a CSS3 full width dropdown menu, but some details i can't get right. :-(

What i try to achieve is this:

You can see there is a little 20px space between the mainmenu and the submenu. In this example i used a top-margin:20px for the ul submenu. But that doesn't really work, because you will leave the hover-area with your cursor and the submenu wil dissapear. The dropdown only works if the ul-container of the submenu "touches" the hover-area.

It did tried using the ul:before trick to add an empty block before the submenu ul, but somehow that doesn't work. :( It doens't take space like a block should do. It's just adding the content right over the ul element.

What do i overlook or doing wrong here? :( Why is the ul ul:after not working? Is there a better way to add a little bit of empty "hoverspace" above the submenu?

Your help would be very helpfull :-).

Live demo: http://jsfiddle.net/JeroenGerth/hDmxd/

The HTML:

<nav>
    <ul id="menu">
        <li><a href="#">Home</a></li>
        <li><a href="#">Tutorials &gt;</a>
            <ul class="submenu">
                <li><a href="#">Photoshop 1</a></li>
                <li><a href="#">Dreamweaver 2</a></li>
                <li><a href="#">Photoshop 3</a></li>
                <li><a href="#">InDesign 4</a></li>
                <li><a href="#">Bridge 5</a></li>
                <li><a href="#">Lightroom 6</a></li>
                <li><a href="#">After Effects 7</a></li>
                <li><a href="#">Premiere 8</a></li>
                <li><a href="#">Motion 9</a></li>
                <li><a href="#">Aperture 10</a></li>
                <li><a href="#">iPhoto 11</a></li>
            </ul>
        </li>
        <li><a href="#">Downloads &gt;</a>
        <ul class="submenu">
                <li><a href="#">Wallpapers 1</a></li>
                <li><a href="#">PSD files 2</a></li>
                <li><a href="#">Video's 3</a></li>
                <li><a href="#">Soundeffects 4</a></li>
                <li><a href="#">Icons 5</a></li>
                <li><a href="#">Maps 6</a></li>
            </ul>
        </li>
        <li><a href="#">About me</a></li>
        <li><a href="#">Contact</a></li>
    </ul>
</nav>

The CSS:

body {background-color: #E9E9E9;}

nav ul { /*Main menu container*/
margin: 0px;
padding: 0px 20px; 
background-color:#444;
color: #fff; 
list-style: none; 
position:relative; 
display:inline-table; 
border-radius: 5px; 
}

nav ul:after {
    content: ""; clear: both; display: block;
}

nav ul li { /*Main menu-items*/ float:left;}

nav ul li a {
    padding: 10px 20px; 
    color: #fff; 
    font-family: Calibri, Verdana, sans-serif; 
    text-decoration:none; 
    display: block; 
    -webkit-transition: all 0.2s ease-in-out;
    -moz-transition: all 0.2s ease-in-out;
    -o-transition: all 0.2s ease-in-out;
    transition: all 0.2s ease-in-out;
    }

    nav ul li a:hover {color: #66D1D3;}

nav ul ul { /*Submenu container*/
display:block; 
border-radius:0px; 
padding: 0px; 
position: absolute; 
background-color:#fff;
color: #000; 
visibility:hidden;
opacity:0;
transition:all ease-in-out 0.4s;
left: 0px;
top: 100%;
width: 100%;
columns:100px 3;
-webkit-columns:100px 3; /* Safari and Chrome */
-moz-columns:100px 3; /* Firefox */
}

        nav ul li:hover > ul { /*Show submenu*/
                visibility:visible;
                opacity:1;
                transition-delay:0s;
                }

nav ul ul:before { /*Why doesn't this work :( */
content: "";
display: block;
height: 20px;
position: absolute;
width: 100%;}

nav ul ul li { /*Submenu items*/
    float: none; 
    border-bottom: 1px #CCCCCC dotted; 
    position:relative; 
            }

    nav ul ul li a {
        color: #000; 
         -webkit-transition: all 1s ease-in-out;
        -moz-transition: all 0.2s ease-in-out;
        -o-transition: all 0.2s ease-in-out;
        transition: all 0.2s ease-in-out;
        }
    nav ul ul li a:hover { 
        color: #66D1D3;
        background-color: #444;
        }

Answer 1

Add a margin-top to nav ul li:hover > ul:

nav ul li:hover > ul { 
    visibility:visible;
    opacity:1;
    transition-delay:0s;
    margin-top: 20px; /* new */
}

Updated fiddle: http://jsfiddle.net/hDmxd/3/

Note: it won't disappear since the easing fadeout gives enough time for the user's mouse to leave the menu and enter the sub-menu.