CSS problem for Stackoverflow

body{
    margin: 0;
    padding: 0;
    background-color: #93ece7;
}
.Wrapper{
    position: relative;
    width: 1200px;
    height: 1000px;
    overflow: auto;
    margin: auto;
    background-color:white;

}
.Header{
    margin: 0;
    background-color: #aaa;
    color: #fff;
}
.Header h1{
    margin: 0px;
    padding:10px 0px 10px 0px;
    text-align: center;
}
.Header p{
    text-align: center;
    position: relative;
    bottom: 25px;
    font-size: 90%
}
.nav{
    position: absolute;
    top: 71.9px;
    left: -39.9px;
    float: right;
}
.nav ul{
    list-style: none;
    float: right;
}
.nav ul li{
}
.nav ul li a{
    text-decoration: none;
    color: black;
    display: block;
    background-color: #aaa;
    padding: 10px;
t;
}
.nav ul li a:hover{
    background-color: #999;
    color: white;
}
.nav ul li span{
    display: block;
    padding: 10px;
    font-size: 104%;
    background-color: #999;
}
.content{
    clear: both;
}