<div id="navi">
                
                 <nav>
            <ul>
                <li class = "cat1">
                    <a href="index.php">Home</a>
                </li>
                <li class = "cat2">
                    <a href="über uns.php">Über uns</a>
                </li>
                <li class = "cat3">
                     <a href="forum.php">Forum</a>
                </li>
                <li class = "cat4">
                    <a href="events.php">Events</a>
                </li>
                <li class = "cat5">
                    <a href="kontakt.php">Kontakt</a>
                </li>
            </ul>
        </nav>
                
            </div>

 nav {
    width: 1000px;
}
nav ul {
    padding: 0%;
    margin: 0%;
}
nav ul:after {
    clear: both;
    content: " ";
    display: block;
    font-size: 0;
    height: 0;
    visibility: hidden;
}
    nav ul,nav ul li{
    background-color: lightgrey;
}
    nav ul li {
    list-style: none;
    float:left;
}
nav ul li a {
    text-decoration: none;
    display: block;
    color: #333;
    padding: 14px 34px 14px 34px;
}
nav ul li:hover > ul {
    visibility: visible;
}
nav ul li ul{
    display: inline;
    visibility: hidden;
    position: absolute;
    padding:0px;
}
nav ul li ul li{
    float: none;
}
nav ul li ul li a:hover{
    color: #333;
}
    
    nav ul {
    padding: 0px;
    margin: 0px;
 
    box-shadow: 2px 2px 2px #dfdfdf;
    -moz-box-shadow: 2px 2px 2px #dfdfdf;
    -webkit-box-shadow: 2px 2px 2px #dfdfdf;
}
nav ul li {
list-style: none;
    float:left;
    border-right: 1px solid #dfdfdf;
}
nav ul li a {
    text-decoration: none;
    display: block;
    color: #333;
    padding: 14px 34px 14px 34px;
    
 
    -webkit-transition: background 0.3s ease-out 0s;
    -moz-transition: background 0.3s ease-out 0s;
    -o-transition: background 0.3s ease-out 0s;
    transition: background 0.3s ease-out 0s;
}
nav ul li.cat1:hover a, nav ul li.cat1:hover > ul li a  {
    background-color: dimgray;
}
nav ul li.cat2:hover a, nav ul li.cat2:hover > ul li a  {
    background-color: dimgray;
}
nav ul li.cat3:hover a, nav ul li.cat3:hover > ul li a {
    background-color: dimgray;
}
nav ul li.cat4:hover a, nav ul li.cat4:hover > ul li a {
    background-color: dimgray;
}
nav ul li.cat5:hover a, nav ul li.cat5:hover > ul li a {
    background-color: dimgray;
}

nav ul li:hover > a {
    color: #FAFAFA;
}
nav ul li ul li a {
    color: #FAFAFA;
}
nav ul li ul li a:hover {
    color: #333;
    background-color: #FAFAFA !important;
}