body {
    margin: 0;
    background-color: #d3d3d3;
    font-family: sans-serif;
    color: #111;
  }
  
  header {
    background-color: #c0c0c0;
    display: flex;
    justify-content: center;
    padding: 1em;
    border-bottom: 2px solid #000;
  }
  
  .nav-btn {
    margin: 0 1em;
    padding: 0.5em 1em;
    border: 2px solid #000;
    background: #e0e0e0;
    cursor: pointer;
    text-decoration: none;
    color: #000;
    font-weight: bold;
}

.nav-btn:hover {
    background-color: #c0c0c0;
}

  
  main {
    padding: 2em;
    text-align: center;
  }
  
  ul {
    list-style-type: none;
    padding: 0;
  }
  
  ul li {
    margin: 1em 0;
  }