body {
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
  }
  
  header {
    background-color: #2F4F7F;
    color: #fff;
    padding: 20px;
    text-align: center;
  }
  
  header nav ul {
    list-style: none;
    margin: 0;
    padding: 0;
  }
  
  header nav li {
    display: inline-block;
    margin-right: 20px;
  }
  
  header nav a {
    text-decoration: none;
    color: #fff;
  }
  
  header nav a:hover {
    color: #ccc;
  }
  
  main {
    max-width: 800px;
    margin: 40px auto;
    padding: 20px;
  }
  
  main section {
    margin-bottom: 40px;
  }
  
  main h2 {
    font-size: 24px;
  }
  
  main p {
    font-size: 16px;
  }
  
  footer {
    background-color: #2F4F7F;
    color: #fff;
    padding: 10px;
    text-align: center;
  }

  .pc-skill, .lesson-pics {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
  }

  .home-h2 {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
  }

  .lesson-pics {
    max-width: 55%;
    height: auto;
  }

  .but {
    background-color: #2F4F7F;
    color: white;
    border: none;
    padding: 15px 32px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 16px;
    cursor: pointer;
    outline: none;
    box-shadow: 0 5px #999;
  }

  .but:hover {background-color: #051a39}

  .but:active {
    background-color: #2F4F7F;
    box-shadow: 0 5px #666;
    transform: translateY(4px);
  }

  .container {
    height: 75px;
    position: relative;
  }
  
  .center {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
  }