html {
    font-family: sans-serif;
  }
  
  header {
    background-color: #333;
    overflow: hidden;
  }
  
  header a {
    float: left;
    color: #f2f2f2;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 17px;
  }
  
  header a:hover {
    background-color: #ddd;
    color: black;
  }
  
  header a:active {
    background-color: #FFFFFF;
    color: white;
  }