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<p>Look ma, no JavaScript!</p>
<p><small>(If you're all about the markup and don't mind a tiny bit of JS, check <a target="_blank" href="https://codepen.io/eduardoboucas/pen/rayExg">this one</a>.)</small></p>
<input class="burger-check" id="burger-check" type="checkbox"><label for="burger-check" class="burger"></label>
<nav id="navigation1" class="navigation">
  <ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">Stuffs</a></li>
    <li><a href="#">Other stuffs</a></li>
    <li><a href="#">Cats</a></li>
  </ul>
</nav>

<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>

// Burger menu button
html {
  background:black;
}
$burger--thickness: 4px;
.burger {
	$width: 28px;
	
	display: inline-block;
  border: 0;
	background: none;
	outline: 0;
	padding: 0;
	cursor: pointer;

	border-bottom: $burger--thickness solid currentColor;
	width: $width;

	transition: border-bottom 1s ease-in-out;
	-webkit-transition: border-bottom 1s ease-in-out; 

	// Fix for extra space in Firefox
	&::-moz-focus-inner {
		border: 0;
		padding: 0;
	}	 

	&:before {
		content: "";
		display: block;
		border-bottom: $burger--thickness solid currentColor;
		width: 100%;
		margin-bottom: 5px;
		transition: transform 0.5s ease-in-out;    
		-webkit-transition: -webkit-transform 0.5s ease-in-out;        
	}

	&:after {
		content: "";
		display: block;
		border-bottom: $burger--thickness solid currentColor;
		width: 100%;
		margin-bottom: 5px;
		transition: transform 0.5s ease-in-out;
		-webkit-transition: -webkit-transform 0.5s ease-in-out;
	}
}

.burger-check {
  display: none;
}

.burger-check:checked ~ .burger {
  border-bottom: $burger--thickness solid transparent;
  transition: border-bottom 0.8s ease-in-out;
  -webkit-transition: border-bottom 0.8s ease-in-out;

  &:before {
    transform: rotate(-405deg) translateY(1px) translateX(-3px);
    -webkit-transform: rotate(-405deg) translateY(1px) translateX(-3px);      
    transition: transform 0.5s ease-in-out;
    -webkit-transition: -webkit-transform 0.5s ease-in-out;
  }

  &:after {
    transform: rotate(405deg) translateY(-4px) translateX(-5px); 
    -webkit-transform: rotate(405deg) translateY(-4px) translateX(-5px);       
    transition: transform 0.5s ease-in-out;
    -webkit-transition: -webkit-transform 0.5s ease-in-out;
  }
}

// * * * Navigation * * *
$navigation__transition: max-height 0.5s ease-in-out;

.navigation {
  overflow: hidden;
  max-height: 0;
  
  transition: $navigation__transition;
}

.burger-check:checked ~ .navigation {
  max-height: 500px;
  
  transition: $navigation__transition;
}

// * * * Demo * * *
body {
  background-color: floralwhite;
  font-family: 'Libre Baskerville', serif;
  font-style: italic;
  font-size: 30px;
  text-align: centeR;
}

a {
  color: inherit;
}

small {
  font-size: 14px;
}

ul {
  margin: 0;
  padding: 0;
}

li {
  list-style: none;
  font-size: 25px;
  padding: 5px 0;
  
  a {
    text-decoration: none;

    &:hover {
      text-decoration: underline;
    }    
  }
}

<link href="https://fonts.googleapis.com/css?family=Libre+Baskerville:400italic" rel="stylesheet" />