MENÜ automatisch schließen

/*################_MENU_NEW_###################*/

#full-screen-menu-toggle {
    z-index: 200;
    position: fixed;
    padding: 0.25em 0.5em;
    top:1em;
    right:1em;
    background: rgba(0,6,22, 0.75);
    color: #FFFFFF;
    font-weight: 400;
}

.full-screen-menu-active #full-screen-menu-toggle {
    background:red;
}


.site-nav {
  transition: all 0.4s ease;
  opacity: 0;
  pointer-events: none;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 6, 22, 0.85);
  z-index:100;
  width: 181px;
  height: 272px;
}


.full-screen-menu-active .site-nav {
  opacity: 1;
  pointer-events: initial;
}

.site-nav ul {
  display: block;
  transition: all 0.3s ease;
  padding: 0;
  list-style-type: none!important;
  position: absolute;
  top: 60%;
  left: 50%;
  transform: translate(-50%, -50%) scale(1.3);
  margin: 0px!important;
  padding: 0px!important;
  color: #FFFFFF;
  font-weight: 400!important;
}

.site-nav a {
    color:white;
    text-decoration: none;
    display: block;
    padding:.5em;
}


.full-screen-menu-active .site-nav ul {
  transform: translate(-50%, -50%) scale(0.9)
}

/*############*/

<nav class="site-nav">
  <ul>
        <li style="list-style-type: none; margin-bottom: 3px; line-height: 1em;"><a href="#UE">&blacksquare;&nbsp;&nbsp;Über mich</a></li>
        <li style="list-style-type: none; margin-bottom: 3px; line-height: 1em;"><a href="#Leistungen">&blacksquare;&nbsp;&nbsp;Leistungen</a></li>
        <li style="list-style-type: none; margin-bottom: 3px; line-height: 1em;"><a href="#Kurse">&blacksquare;&nbsp;&nbsp;Kurse</a></li>
        <li style="list-style-type: none; margin-bottom: 3px; line-height: 1em;"><a href="#Kontakt">&blacksquare;&nbsp;&nbsp;Kontakt</a></li>
        <li style="list-style-type: none; margin-bottom: 3px; line-height: 1em;"><a href="#Recht">&blacksquare;&nbsp;&nbsp;Rechtliche Hinweise</a></li>
  </ul>
</nav>


    <div id="full-screen-menu-toggle" style=" font-size: 1.5em;">&Congruent;</div>


<script> 
  // Quelle: http://johnm.io/project/hamburgler/
  
  document.getElementById('full-screen-menu-toggle').addEventListener('click', checkNav);
  window.addEventListener("keyup", function(e) {
    if (e.keyCode == 27) closeNav();
  }, false);

  function checkNav() {
    if (document.body.classList.contains('full-screen-menu-active')) {
      closeNav();
    } else {
      openNav();
    }
  }

  function closeNav() {
    document.body.classList.remove('full-screen-menu-active');
  }

  function openNav() {
    document.body.classList.add('full-screen-menu-active');
  }
</script>