.topnav {
  overflow: hidden;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.topnav a {
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 20px;
}

.topnav a:hover {
  background-color: #ddd;
  color: black;
}

.topnav a.active {
  background-color: #FFA500;
  color: white;
}

body {
  margin: 0;
  padding: 0;
  background-image: url('https://images.wallpaperscraft.com/image/single/planet_craters_space_61032_1280x720.jpg');
  background-repeat: no-repeat;
  background-size: cover;
  background-position: center center;
  background-attachment: fixed;
  color: white;
  font-family: Arial, sans-serif;
  min-height: 100vh;
}


@media screen and (max-width: 600px) {
  .topnav a {
    font-size: 16px;
    padding: 10px;
  }

  body {
    background-position: top center;
    background-attachment: scroll;
  }
}