Pure CSS Hamburger fold-out menu by Erik Terwan

<!--    Made by Erik Terwan    -->
<!--   24th of November 2015   -->
<!--        MIT License        -->
<nav role="navigation">
  <div id="menuToggle">
    <!--
    A fake / hidden checkbox is used as click reciever,
    so you can use the :checked selector on it.
    -->
    <input type="checkbox" />

    <!--
    Some spans to act as a hamburger.
    
    They are acting like a real hamburger,
    not that McDonalds stuff.
    -->
    <span></span>
    <span></span>
    <span></span>

    <!--
    Too bad the menu has to be inside of the button
    but hey, it's pure CSS magic.
    -->
    <ul id="menu">
      <a href="#"><li>Home</li></a>
      <a href="#"><li>About</li></a>
      <a href="#"><li>Info</li></a>
      <a href="#"><li>Contact</li></a>
      <a href="https://erikterwan.com/" target="_blank"
        ><li>Show me more</li></a
      >
    </ul>
  </div>
</nav>

/*
 * Made by Erik Terwan
 * 24th of November 2015
 * MIT License
 *
 *
 * If you are thinking of using this in
 * production code, beware of the browser
 * prefixes.
 */
body {
  margin: 0;
  padding: 0;
  /* make it look decent enough */
  background: #232323;
  color: #cdcdcd;
  font-family: 'Avenir Next', 'Avenir', sans-serif;
}

a {
  text-decoration: none;
  color: #232323;
  transition: color 0.3s ease;
}

a:hover {
  color: tomato;
}

#menuToggle {
  display: block;
  position: relative;
  top: 50px;
  left: 50px;
  z-index: 1;
  -webkit-user-select: none;
  user-select: none;
}

#menuToggle input {
  display: block;
  width: 40px;
  height: 32px;
  position: absolute;
  top: -7px;
  left: -5px;
  cursor: pointer;
  opacity: 0; /* hide this */
  z-index: 2; /* and place it over the hamburger */
  -webkit-touch-callout: none;
}

/*
 * Just a quick hamburger
 */
#menuToggle span {
  display: block;
  width: 33px;
  height: 4px;
  margin-bottom: 5px;
  position: relative;
  background: #cdcdcd;
  border-radius: 3px;
  z-index: 1;
  transform-origin: 4px 0px;
  transition: transform 0.5s cubic-bezier(0.77, 0.2, 0.05, 1), background 0.5s
      cubic-bezier(0.77, 0.2, 0.05, 1), opacity 0.55s ease;
}

#menuToggle span:first-child {
  transform-origin: 0% 0%;
}

#menuToggle span:nth-last-child(2) {
  transform-origin: 0% 100%;
}

/* 
 * Transform all the slices of hamburger
 * into a crossmark.
 */
#menuToggle input:checked ~ span {
  opacity: 1;
  transform: rotate(45deg) translate(-2px, -1px);
  background: #232323;
}

/*
 * But let's hide the middle one.
 */
#menuToggle input:checked ~ span:nth-last-child(3) {
  opacity: 0;
  transform: rotate(0deg) scale(0.2, 0.2);
}

/*
 * Ohyeah and the last one should go the other direction
 */
#menuToggle input:checked ~ span:nth-last-child(2) {
  transform: rotate(-45deg) translate(0, -1px);
}

/*
 * Make this absolute positioned
 * at the top left of the screen
 */
#menu {
  position: absolute;
  width: 300px;
  margin: -100px 0 0 -50px;
  padding: 50px;
  padding-top: 125px;
  background: #ededed;
  list-style-type: none;
  -webkit-font-smoothing: antialiased;
  /* to stop flickering of text in safari */
  transform-origin: 0% 0%;
  transform: translate(-100%, 0);
  transition: transform 0.5s cubic-bezier(0.77, 0.2, 0.05, 1);
}

#menu li {
  padding: 10px 0;
  font-size: 22px;
}

/*
 * And let's slide it in from the left
 */
#menuToggle input:checked ~ ul {
  transform: none;
}