body {
    font-family: Arial;
    font-size: 20px;
    color: white;
}
body {
    background-image: url("images/blue.jpg");
}
section {
    text-align: center;
}
section img {
    width: 35%;
}
ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #333;
  position: -webkit-sticky; /* Safari */
  position: sticky;
  top: 0;
}

li {
  float: center;
}

li a {
  display: block;
  color: white;
  text-align: center;
  padding: 8px 12px;
  text-decoration: none;
}

/* Change the link color to #111 (black) on hover */
li a:hover {
  background-color: #111;
}
.active {
  background-color: dodgerblue;
}