html {
  font-family: Arial, Helvetica, sans-serif;
}

.header {
  overflow: hidden;
  background-color: #f1f1f1;
  padding: 20px 10px;
}

.header a {
  float: left;
  color: black;
  text-align: center;
  padding: 12px;
  text-decoration: none;
  font-size: 18px;
  line-height: 25px;
}

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

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

footer {
  position: fixed;
  width: 100%;
  display: block;
  padding: 12px;
  bottom: 0;
  margin-right: 8px;
  background-color: #f1f1f1;
}