html {
  color: #222;
  font-size: 1em;
  line-height: 1.4;
}

body {
  background-color: #001000;
  color: lawngreen;
  margin: 0 10em;
  font-family: consolas, 'Lucida Console', monospace;
}

h1 {
  text-align: center;
  overflow-wrap: anywhere;
}

nav {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: space-evenly;
  align-items: stretch;
}

nav a {
  color: lawngreen;
  text-decoration: none;
  padding: 10px 20px;
  display: inline-block;
}

nav a.active {
  background-color: darkgreen;
}

nav a.active:hover {
  background-color: limegreen;
  animation-name: animateNavActiveHover;
  animation-duration: 0.3s;
}

nav a:hover {
  background-color: limegreen;
  animation-name: animateNavHover;
  animation-duration: 0.5s;
}

@keyframes animateNavHover {
  from {background-color: black;}
  to {background-color: limegreen;}
}

@keyframes animateNavActiveHover {
  from {background-color: darkgreen;}
  to {background-color: limegreen;}
}

main {

}

main p {
  padding: 0;
  margin: 0;
}

hr {
  display: block;
  height: 1px;
  border: 0;
  border-top: 1px solid #ccc;
  margin: 1em 0;
  padding: 0;
}

fieldset {
  border: 0;
  margin: 0;
  padding: 0;
}

textarea {
  resize: vertical;
}

.visually-hidden.focusable:active,
.visually-hidden.focusable:focus {
  clip: auto;
  height: auto;
  margin: 0;
  overflow: visible;
  position: static;
  white-space: inherit;
  width: auto;
}

.invisible {
  visibility: hidden;
}

.lesson-nav {
  position: relative;
}

.lesson-popup {
  display: none;
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  top: 100%;
  background: #222;
  color: lawngreen;
  border: 1px solid lawngreen;
  padding: 1em;
  min-width: 200px;
  z-index: 10;
  box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}

.lesson-nav:hover .lesson-popup,
.lesson-nav:focus-within .lesson-popup {
  display: block;
}

.lesson-popup a {
  color: lawngreen;
  text-decoration: underline;
  display: block;
  margin-bottom: 0.5em;
}

.lesson-popup a:last-child {
  margin-bottom: 0;
}

.code {
  background-color:gainsboro;
  color:black;
  font-family:monospace;
  padding:10px;
}

section {
  padding: 1em;
  border: 1px dashed lawngreen;
  background-color: #000000;
  margin: 2em 0;
}

audio,
canvas,
iframe,
img,
svg,
video {
  vertical-align: middle;
}

@media only screen and (max-width: 305px) {
  h1 {
    font-size: 1em;
  }
}

@media only screen and (max-width: 745px) {
  body {
    margin: 0 1rem;
  }
}

@media only screen and (max-width: 955px) {
  nav {
    flex-direction: column;   /* stack nav items */
    align-items: stretch;
    gap: 0.25rem;
  }

  nav a {
    display: block;
    text-align: center;
    padding: 0.75rem 1rem;
  }
}

/* print only below this line */

@media print,
  (-webkit-min-device-pixel-ratio: 1.25),
  (min-resolution: 1.25dppx),
  (min-resolution: 120dpi) {
  /* Style adjustments for high resolution devices */
}

@media print {
  *,
  *::before,
  *::after {
    background: #fff !important;
    color: #000 !important;
    /* Black prints faster */
    box-shadow: none !important;
    text-shadow: none !important;
  }

  a,
  a:visited {
    text-decoration: underline;
  }

  a[href]::after {
    content: " (" attr(href) ")";
  }

  abbr[title]::after {
    content: " (" attr(title) ")";
  }

  /*
   * Don't show links that are fragment identifiers,
   * or use the `javascript:` pseudo protocol
   */
  a[href^="#"]::after,
  a[href^="javascript:"]::after {
    content: "";
  }

  pre {
    white-space: pre-wrap !important;
  }

  pre,
  blockquote {
    border: 1px solid #999;
    page-break-inside: avoid;
  }

  tr,
  img {
    page-break-inside: avoid;
  }

  p,
  h2,
  h3 {
    orphans: 3;
    widows: 3;
  }

  h2,
  h3 {
    page-break-after: avoid;
  }
}