html, body {
    min-width: 290px;
    color: #4d4e53;
    background-color: #fff;
    font-family: 'Open Sans', Arial, sans-serif;
    line-height: 1.5;
  }

  /*Navigation bar style*/
  
  #navbar {
    position: fixed;
    min-width: 290px;
    top: 0px;
    left: 0px;
    width: 300px;
    height: 100%;
    border-right: solid;
    border-color: rgba(0, 22, 22, 0.4);
  }
  
  header {
    color: black;
    margin: 10px;
    text-align: center;
    font-size: 1.8em;
  }
  
  #navbar ul {
    height: 88%;
    padding: 0;
    overflow-y: auto;
    overflow-x: hidden;
  }
  
  #navbar li {
    color: #4d4e53;
    border-top: 1px solid;
    list-style: none;
    position: relative;
    width: 100%;
  }
  
  #navbar a {
    display: block;
    padding: 10px 30px;
    color: #4d4e53;
    text-decoration: none;
    cursor: pointer;
  }
  
  #navbar li .sub-item{
    padding-left: 40px;
  }

  #navbar li i {
    margin-right: 15px;
  }
  
  #navbar li .nav-link:hover {
    color: #fff;
    background: #632ed0;
    transition: 0.3s ease;
  }

  #navbar li .dropdown {
    position: absolute;
    right: 20px;
    margin: 3px;
    transition: 0.3s ease;
  }

  #navbar li .sub-menu {
    background: rgba(255, 255, 255, 0.1);
    display: none;
  }
  
  .rotate {
    transform: rotate(90deg);
  }
  
  /*Content Page style*/

  #main-doc {
    position: absolute;
    margin-left: 310px;
    padding: 20px;
    margin-bottom: 110px;
  }
  
  #main-doc header {
    text-align: left;
    margin: 0;
  }
  
  section article {
    color: #4d4e53;
    margin: 15px;
    font-size: 0.96em;
  }
  
  section li {
    margin: 15px 0px 0px 20px;
  }

  a:link, a:visited {
    color: #001e4d;
  }

  a:hover {
    color: #632ed0;
  }

  /* code box style */
  
  code {
    display: block;
    text-align: left;
    white-space: pre-line;
    position: relative;
    word-break: normal;
    word-wrap: normal;
    line-height: 2;
    background-color: #f7f7f7;
    padding: 15px;
    margin: 10px;
    border-radius: 5px;
  }

  /* image styles */

  .img {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: auto;
    height: 200px;
  }

  #massimo {
    display: inline;
    height: 400px;
  }

  #arduino_parts {
    display: inline;
    width: 500px;
    height: auto;
  }
  /* Quiz Style*/

  .app {
    background: #001e4d;
    width: 90%;
    max-width: 500px;
    margin: 15px auto 0;
    border-radius: 10px;
    padding: 45px;
  }

  .app h1 {
    font-size: 25px;
    color: #fff;
    font-weight: 600;
    border-bottom: 1px solid #333;
    padding-bottom: 10px;
  }

  .quiz h2 {
    font-size: 18px;
    color: #fff;
    font-weight: 600;
  }

  .btn {
    background: #fff;
    color: #222;
    font-weight: 500;
    width: 100%;
    border: 1px solid #222;
    padding: 10px;
    margin: 10px 0;
    text-align: left;
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.3s;
  }

  .btn:hover:not([disabled]) {
    background: #632ed0;
    color: #fff;
  }

  .btn:disabled {
    cursor: no-drop;
  }

  #next-btn {
    background: #632ed0;
    color: #fff;
    font-weight: 500;
    width: 150px;
    border: 0;
    padding: 10px;
    margin: 20px auto 0;
    border-radius: 4px;
    cursor: pointer;
    display: none;
  }

  .correct {
    background: #9aeabc;
  }
  
  .incorrect {
    background: #ff9393;
  }

  /* responsive style */
  
  @media (max-width: 700px) {
    body {
      flex-direction: column;
    }
    #navbar {
      position: relative;
      width: 100%;
    }
    .nav-link {
      font-size: 1rem;
    }
    p {
      width: 100%;
    }
    #main-doc {
      width: 100%;
      margin-left: 0;
    }
    .img {
      width: 50%;
    }
  }