<body>
  
  <a href="#" class="button">
    <span class="menu">
      <b>menu</b>
    </span>
  </a>
  
  <ul class="sub-menu">
    <li>Home</li>
    <li>About</li>
    <li>Blog</li>
    <li>Contact</li>
  </ul>
  
</body>
@import url(https://fonts.googleapis.com/css?family=Open+Sans:600,300);

%line{
  background: white;
  width:30px;
  height:3px;
}

// Animate the top bar on hover
@keyframes menu-hover-top-over {
  0% {
    transform: translateY(0);
  }
  50%{
    transform: translateY(8px);
  }
  100%{
    transform: translateY(0);
  }
}

// Animate the bottom bar on hover
@keyframes menu-hover-bottom-over {
  0% {
    transform: translateY(0);
  }
  50%{
    transform: translateY(-8px);
  }
  100%{
    transform: translateY(0);
  }
}

// Animate the top bar on hover-OUT
@keyframes menu-load-state-top{
  0% {
    transform: translateY(0);
  }
  50%{
    transform: translateY(8px);
  }
  100%{
    transform: translateY(0);
  }
}

// Animate the bottom bar on hover-OUT
@keyframes menu-load-state-bottom{
  0% {
    transform: translateY(0);
  }
  50%{
    transform: translateY(-8px);
  }
  100%{
    transform: translateY(0);
  }
}


//Slide that sub-menu in
@keyframes menu-active-slide {
  0% {
    transform: translateX(-10px);
  }
  100%{
    transform: translateX(0);
  }
}

//Rotate that top bar on active
@keyframes top-rot-in {
  0% {
    transform: rotate(0deg);
    transform-origin: left;
  }
  100% {
    transform: rotate(45deg);
    transform-origin: left;
 
  }
}
//Rotate that bottom bar on active
@keyframes bot-rot-in {
  0% {
    transform: rotate(0deg);
    transform-origin: left;
  }
  100% {
    transform: rotate(-45deg);
    transform-origin: left;
 
  }
}

body{
  font-family: 'Open Sans', sans-serif;
  color:white;
  a{
    color:white;
    text-decoration:none;
  }
}

.button{
  padding:10px;
  height:30px;
  width:30px;
  display:block;
  position: relative;
  background: #ed2fd3; /* Old browsers */
  background: linear-gradient(135deg,  #ed2fd3 0%,#001e8e 100%); /* W3C */
}

.menu{
  @extend %line;
  position: absolute;
  top: 24px;
  &:before{
    @extend %line;
    content: '';
    position: absolute;
    top: -8px;
    animation:  menu-load-state-top .5s;
  }
  &:after{
    @extend %line;
    content: '';
    position: absolute;
    top: 8px;
    left:0px;
    animation:  menu-load-state-bottom .5s;
  }
  b{
    opacity:0;
    top:-13px;
    left:2px;
    font-size:.55em;
    line-height:1em;
    position:relative;
    transition: all 0.15s 0.15s ease-in;
    transition-delay: .5s;
  }
}

.menu:hover{
  background: transparent;
  transition: all 0.15s 0 ease-out;
  &:before{
    animation: menu-hover-top-over .5s .5s forwards;
  }
  &:after{
    animation: menu-hover-bottom-over .5s .5s forwards;
  }
  b{
    opacity:1;
  }
}

///Lets make a sub-menu
.sub-menu{
  font-weight:300;
  font-size:1.5em;
  list-style-type:none;
  padding:10px 20px;
  width:200px;
  background: #001e8e; /* Old browsers */
  background: linear-gradient(to bottom,  #001e8e 0%,#ed2fd3 100%); /* W3C */
  margin:0;
  position:fixed;
  top:8px;
  left:65px;
  transition: opacity 0.25s ease;
  opacity:0;
  li{
    line-height:60px;
    border-bottom:1px solid white;
  }
  li:last-child{
    border-bottom:none;
  }
}

.active{
  .menu{
    background:transparent;
    &:before{
      top: -10px;
      left:5px;
      animation: top-rot-in .5s forwards;
    }
    &:after{
      top: 10px;
      left:5px;
      animation: bot-rot-in .5s forwards;
    }
    b{
      opacity:0;
      transition: all 0.10s 0 ease-out;
    }    
  }
  .sub-menu{
    opacity:1;
    transition: opacity 0.25s ease;
    animation: menu-active-slide .25s;
  }
}
View Compiled
$(".button").click(function(){
 $(this).closest("body").toggleClass("active");
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js