@media screen {
  html, body {
    margin: 0;
    padding: 0;
  }

  .container {
    margin: 0 auto;
    max-width: 680px;
    padding: 0 20px;
  }

  nav {
    margin: 2em 0;
    display: flex;
    align-items: center;
    justify-content: space-between;
  }

  nav a {
    text-decoration: none;
    color: var(--heading-color);
  }

  nav a.prev, nav a.next {
    font-size: 3em;
    text-decoration: none;
    color: var(--heading-color);
  }
  
  nav .lesson-nav {
    display: flex;
    flex-direction: column;
  }

  nav h1 {
    font-size: 1.2em;
    margin: 0;
    margin-bottom: .5em;
    text-align: center;
    position: relative;
  }
  
  nav .dropdown-trigger {
    cursor: pointer;
    padding: 0 1em;
  }

  nav .dropdown-trigger:hover {
    border: 1px solid var(--box-border-color);
    border-radius: 4px;
  }

  nav .dropdown {
    position: absolute;
    background: white;
    z-index: 1;
    padding: 10rem 20rem;
    width: auto;
    box-shadow: 0px 4px 8px rgba(0, 0, 0, 0.3);
    text-align: left;
    margin-top: .25em;
    font-size: var(--base-font-size);
    display: none;
  }

  nav .dropdown:focus {
    outline: none;
  }

  nav .dropdown.active {
    display: block;
  }

  nav .dropdown li {
    list-style-type: none;
    line-height: 1.5em;
    cursor: pointer;
    white-space: nowrap;
  }

  nav .dropdown li:hover {
    text-decoration: underline;
  }

  nav .activities {
    margin: 0;
    padding: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-wrap: wrap;
  }

  nav .activities li {
    list-style-type: none;
    padding: 0;
  }
  nav .activities li:before {
    display: none; 
  }

  nav .activities li a {
    --size: 1.2em;
    font-size: var(--size);
    width: calc(var(--size) * 1.2);
    height: calc(var(--size) * 1.2);
    margin: 0 .25em;
    border: 1px solid black;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    vertical-align: middle;
    border-radius: 100%;
  }

  nav .activities li.active a {
    background: var(--heading-color);
    color: white;
  }
}