body {
  background-image: url(images/marble.jpg);
  text-align: center;
}
.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
}
  }
.nav{
    border:1px solid #ccc;
    border-width:1px 0;
    list-style:none;
    margin:0;
    padding:0;
    text-align:center;
}
.nav li{
    display:inline;
}
.nav a{
    display:inline-block;
    padding:10px;
}
footer {
    text-align: center; 
}