Fullscreen Hamburger Mega Menu With JS And CSS

A hamburger mega menu with an animated fullscreen overlay built with JavaScript and CSS/CSS3.

How to use it:

Create the fullscreen mega menu with a close button.

<nav id="overlay">
  <img src="images/close-button.svg" alt="menu" class="close-button"  id="close-menu">
  <ul>
      <li>
          <a href="#">Home</a>
          <span>Watch out, This is my site</span>
      </li>
      <li>
          <a href="#">About Me</a>
          <span>Watch out, This is my site</span>
      </li>
      <li>
          <a href="#">Services</a>
          <span>Watch out, This is my site</span>
      </li>
      <li>
          <a href="#">Contact</a>
          <span>Watch out, This is my site</span>
      </li>
  </ul>
</nav>

Create a hamburger button to toggle the mega menu.

<img src="images/burger-menu.svg" alt="menu" class="menu-btn" id="open-menu">

Style the mega menu in the CSS.

nav .close-button {
  width: 18px;
  float: right;
  cursor: pointer;
  opacity: 0;
}
nav ul {
  list-style-type: none;
  margin: 10% auto 0 auto;
  padding: 0;
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: (auto)[4];
      grid-template-columns: repeat(4, auto);
  width: 80%;
}
nav ul a {
  color: white;
  font-weight: bold;
  font-size: 1.4em;
}
nav ul span {
  color: gray;
  display: block;
  font-size: .75em;
  margin-top: 20px;
}
nav ul li {
  opacity: 0;
}

The necessary CSS/CSS3 rules for the animated overlay.

.show-menu {
  display: block;
  -webkit-animation: slide-menu 1s ease-in forwards;
          animation: slide-menu 1s ease-in forwards;
}
.show-menu .close-button {
  -webkit-animation: show-x 1s 1s forwards;
          animation: show-x 1s 1s forwards;
}
.show-menu li:nth-of-type(1) {
  -webkit-animation: menu-item-anim .6s forwards 1s ease-in-out;
          animation: menu-item-anim .6s forwards 1s ease-in-out;
}
.show-menu li:nth-of-type(2) {
  -webkit-animation: menu-item-anim .6s forwards 1.2s ease-in-out;
          animation: menu-item-anim .6s forwards 1.2s ease-in-out;
}
.show-menu li:nth-of-type(3) {
  -webkit-animation: menu-item-anim .6s forwards 1.6s ease-in-out;
          animation: menu-item-anim .6s forwards 1.6s ease-in-out;
}
.show-menu li:nth-of-type(4) {
  -webkit-animation: menu-item-anim .6s forwards 1.8s ease-in-out;
          animation: menu-item-anim .6s forwards 1.8s ease-in-out;
}
@-webkit-keyframes slide-menu {
  from {
    -webkit-transform: scaleX(0);
            transform: scaleX(0);
  }
  to {
    -webkit-transform: scaleX(1);
            transform: scaleX(1);
  }
}
@keyframes slide-menu {
  from {
    -webkit-transform: scaleX(0);
            transform: scaleX(0);
  }
  to {
    -webkit-transform: scaleX(1);
            transform: scaleX(1);
  }
}
@-webkit-keyframes show-x {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}
@keyframes show-x {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}
@-webkit-keyframes menu-item-anim {
  from {
    -webkit-transform: translateY(70%);
            transform: translateY(70%);
    opacity: 0;
  }
  to {
    -webkit-transform: translateY(0);
            transform: translateY(0);
    opacity: 1;
  }
}
@keyframes menu-item-anim {
  from {
    -webkit-transform: translateY(70%);
            transform: translateY(70%);
    opacity: 0;
  }
  to {
    -webkit-transform: translateY(0);
            transform: translateY(0);
    opacity: 1;
  }
}

Activate the mega menu by toggling CSS classes using JavaScript.

const overlay = document.getElementById('overlay');
const closeMenu = document.getElementById('close-menu');

document.getElementById('open-menu') .addEventListener('click', function() {
    overlay.classList.add('show-menu');
});
document.getElementById('close-menu').addEventListener('click', function(){
    overlay.classList.remove('show-menu')
})