@media all and (max-width: 1000px) {
  footer {
      text-align: center;
  }
}

@media all and (max-width: 900px) {
  .introduction {
    height: 900px;
  }
  
  .lessons {
    flex-wrap: wrap;
  }

  .introduction h1 {
    padding-bottom: 0;
  }

  .lesson {
    margin: 100px auto 20px;
  }
}

@media all and (max-width: 750px) {
  .top-wrapper h1 {
    font-size: 32px;
  }

  .heading h2 {
    font-size: 20px;
  }
}

@media all and (max-width: 670px) {
  .nav-bar {
    display: flex;
    justify-content: space-between;
  }
  .right-bar {
    display: none;
  }

  .menu-icon {
    display: block;
    margin-right: 1%;
  }

  .container {
    text-align: left;
  }

  .container h1 {
    font-size: 24px;

  }

  .container p {
    font-size: 14px;
  }

  .top-wrapper .btn {
    width: 100%;
    padding: 8px 2px;
  }

  .twitter {
    margin-top: 10px;
  }

  .introduction {
    height: 1500px;
  }
  
}