body {
    background-color: rgb(255, 255, 255);
    margin:0;
  }

  .center {
    text-align: center;
    display: block;
    margin-left: auto;
    margin-right: auto;
  }

  ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
    position: fixed;
    top: 0;
    width: 100%;
  }
  
  li {
    float: left;
  }
  
  li a {
    display: block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
  }
  
  li a:hover:not(.active) {
    background-color: #6d6d6d;
  }
  
  .active {
    background-color: #4d6c7a;
  }