Morphing Side Menu with Pure CSS / CSS3

A Material Design inspired morphing menu that uses CSS3 transitions and transforms to transform a menu toggle into a side menu with smooth transitions.

Basic usage:

Create a checkbox that allows you to open/close the side menu.

<input type="checkbox" id="menuTrigger">

Create a side menu with a hamburger toggle.

<div class="menu">
  <h3>Contact us</h3>
  <label for="menuTrigger" class="trigger">
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
  </label>
  <ul class="links">
    <li class="link"><a href="#">Google+</a></li>
    <li class="link"><a href="#">Facebook</a></li>
    <li class="link"><a href="#">Twitter</a></li>
    <li class="link"><a href="#">CodePen</a></li>
    <li class="link"><a href="#">Github</a></li>
    <li class="link"><a href="#">Linkedin</a></li>
    <li class="link"><a href="#">Pinterest</a></li>
    <li class="link"><a href="#">Instagram</a></li>
    <li class="link"><a href="#">Stumbleupon</a></li>
  </ul>
</div>

The primary CSS for the side menu.

.menu {
  position: absolute;
  top: 0;
  left: 0;
  z-index: 10;
  height: 370px;
  width: 170px;
  overflow: hidden;
  pointer-events: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}
.menu * {
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}
#menuTrigger:checked ~ .menu { pointer-events: auto; }
.menu h3 {
  position: absolute;
  top: 10px;
  left: 10px;
  z-index: 1;
  margin: 0;
  font-size: 1em;
  font-weight: normal;
  line-height: 56px;
  color: white;
  -webkit-transform: translate3d(-170px, 0, 0);
  transform: translate3d(-170px, 0, 0);
  -webkit-transition: -webkit-transform 0.4s ease-in-out;
  transition: transform 0.4s ease-in-out;
}
.menu .links {
  position: relative;
  z-index: 1;
  list-style: none;
  color: white;
  margin: 76px 0 0 0;
  padding: 0;
}
.menu .link {
  font-size: 16px;
  line-height: 1;
  margin: 0;
  padding: 0;
  -webkit-transition: -webkit-transform 0.4s ease-in-out;
  transition: transform 0.4s ease-in-out;
}
.menu .link a {
  display: block;
  color: currentColor;
  padding: 10px;
  text-decoration: none;
}
.menu .link a:hover { background-color: rgba(255, 255, 255, 0.1); }

The CSS/CSS3 styles for the checkbox based menu trigger.

.menu .trigger {
  position: absolute;
  z-index: 0;
  top: 10px;
  left: 10px;
  height: 56px;
  width: 56px;
  border-radius: 100%;
  cursor: pointer;
  pointer-events: auto;
  -webkit-transition: all 0.4s ease-in-out;
  transition: all 0.4s ease-in-out;
  -webkit-transition-property: -webkit-transform, box-shadow;
  transition-property: transform, box-shadow;
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
  box-shadow: 0 0 0 0px #424242;
}
.menu .trigger:before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
  border-radius: inherit;
  overflow: hidden;
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
  -webkit-transition: box-shadow 0.2s 0.4s ease-in-out;
  transition: box-shadow 0.2s 0.4s ease-in-out;
  box-shadow: 0 0 0 28px #424242 inset, 0 0 0 28px #FF5722 inset;
}
#menuTrigger:checked ~ .menu .trigger {
  -webkit-transform: translate3d(94px, 0, 0);
  transform: translate3d(94px, 0, 0);
  box-shadow: 0 0 0 370px #424242;
}
#menuTrigger:checked ~ .menu .trigger:before {
  -webkit-transition-delay: 0s;
  transition-delay: 0s;
  box-shadow: 0 0 0 0 #424242 inset, 0 0 0 28px #FF5722 inset;
}
#menuTrigger:checked ~ .menu .trigger .line:nth-child(1) {
  -webkit-transform: translateY(0) translate3d(-50%, -50%, 0);
  transform: translateY(0) translate3d(-50%, -50%, 0);
}
#menuTrigger:checked ~ .menu .trigger .line:nth-child(3) {
  -webkit-transform: translateY(0) translate3d(-50%, -50%, 0);
  transform: translateY(0) translate3d(-50%, -50%, 0);
}
.menu .trigger .line {
  position: absolute;
  top: 50%;
  left: 50%;
  background: white;
  height: 2px;
  width: 18.66667px;
  -webkit-transform: translate3d(-50%, -50%, 0);
  transform: translate3d(-50%, -50%, 0);
  -webkit-transition: -webkit-transform 0.4s ease-in-out;
  transition: transform 0.4s ease-in-out;
}
.menu .trigger .line:nth-child(1) {
  -webkit-transform: translateY(-5px) translate3d(-50%, -50%, 0);
  transform: translateY(-5px) translate3d(-50%, -50%, 0);
}
.menu .trigger .line:nth-child(3) {
  -webkit-transform: translateY(5px) translate3d(-50%, -50%, 0);
  transform: translateY(5px) translate3d(-50%, -50%, 0);
}
#menuTrigger {
  position: fixed;
  top: 0;
  left: -20px;
}

Add transform animations to each menu links.

#menuTrigger:checked ~ .menu h3 {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
  -webkit-transition-delay: 0.2s;
  transition-delay: 0.2s;
}
#menuTrigger:checked ~ .menu .link {
  -webkit-transition-delay: 0.2s;
  transition-delay: 0.2s;
}
#menuTrigger:checked ~ .menu .link:nth-child(1) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(2) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(3) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(4) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(5) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(6) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(7) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
#menuTrigger:checked ~ .menu .link:nth-child(8) {
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
.menu .link:nth-child(1) {
  -webkit-transform: translate3d(-100%, 0, 0);
  transform: translate3d(-100%, 0, 0);
}
.menu .link:nth-child(2) {
  -webkit-transform: translate3d(-200%, 0, 0);
  transform: translate3d(-200%, 0, 0);
}
.menu .link:nth-child(3) {
  -webkit-transform: translate3d(-300%, 0, 0);
  transform: translate3d(-300%, 0, 0);
}
.menu .link:nth-child(4) {
  -webkit-transform: translate3d(-400%, 0, 0);
  transform: translate3d(-400%, 0, 0);
}
.menu .link:nth-child(5) {
  -webkit-transform: translate3d(-500%, 0, 0);
  transform: translate3d(-500%, 0, 0);
}
.menu .link:nth-child(6) {
  -webkit-transform: translate3d(-600%, 0, 0);
  transform: translate3d(-600%, 0, 0);
}
.menu .link:nth-child(7) {
  -webkit-transform: translate3d(-700%, 0, 0);
  transform: translate3d(-700%, 0, 0);
}
.menu .link:nth-child(8) {
  -webkit-transform: translate3d(-800%, 0, 0);
  transform: translate3d(-800%, 0, 0);
}