body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
}

.topnav {
  list-style-type: none;
    overflow: hidden;
    background-color: #333;
    position: fixed;
    top: 0;
    width: 100%;
    z-index: 10;
}

.topnav a {
  float: left;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 17px;
}

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

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