Expanding Hamburger Menu With Pure CSS

A plain HTML/CSS sliding navigation that expands the hamburger icon into a sidebar menu when toggled.

How to use it:

Create the hamburger menu and insert it together with the checkbox based menu trigger into a container.

<span class="checkbox-container">
  <input class="checkbox-trigger" type="checkbox"  />
  <span class="menu-content">
      <ul>
        <li>Home</li>
        <li>About</li>
        <li>Contact</li>
        <li>Blog</li>
        <li>Social</li>
      </ul>
    <span class="hamburger-menu"></span>
  </span>
</span>

Style the menu content in the CSS.

.checkbox-container {
  display: block;
  float: left;
  width: 50px;
  height: 50px;
  position: relative;
  background: #182825;
}
.menu-content {
  display: flex;
  background: #182825;
  color: white;
  float: left;
}
.menu-content ul {
  display: block;
  padding-left: 0;
  padding-top: 1em;
  padding-bottom: 1em;
  margin: 0;
  width: 0px;
  height: 0px;
  overflow: hidden;
  transition: height 0.3s ease 0.7s, width 0.7s ease;
}
.menu-content ul li {
  list-style: none;
  padding-top: 1em;
  padding-bottom: 1em;
  cursor: pointer;
  transition: color 0.5s, background 0.5s;
}
.menu-content ul li:hover {
  color: #0CD6AD;
  background: #1E332F;
}

Style the hamburger trigger:

.checkbox-trigger {
  opacity: 0;
  position: absolute;
  width: 50px;
  height: 50px;
  left: 0px;
  cursor: pointer;
  z-index: 5;
}
.hamburger-menu, .hamburger-menu::before, .hamburger-menu::after {
  display: block;
  position: absolute;
  background: white;
  width: 40px;
  height: 4px;
  margin: 1.3em 3em;
  transition: background 0.3s;
}
.hamburger-menu::before, .hamburger-menu::after {
  content: '';
  position: absolute;
  margin: -0.7em 0 0;
  transition: width 0.7s ease 0.3s, transform 0.7s ease 0.3s;
}
.hamburger-menu::after { margin-top: 0.7em; }
.hamburger-menu {
  position: relative;
  display: block;
  margin: 0;
  margin-top: 1.45em;
  margin-right: 0.35em;
  margin-left: 0.35em;
  margin-bottom: 1.45em;
  transition: width 0.3s ease;
}

The core CSS hacks to toggle the hamburger menu using checkbox.

.checkbox-trigger:checked { left: 202px; }
.checkbox-trigger:checked + .menu-content .hamburger-menu {
  width: 2em;
  transition: width 0.7s ease 0.7s;
}
.checkbox-trigger:checked + .menu-content .hamburger-menu::before {
  width: 1.2em;
  transform: rotate(-35deg);
  margin-top: -0.4em;
}
.checkbox-trigger:checked + .menu-content .hamburger-menu::after {
  width: 1.2em;
  transform: rotate(35deg);
  margin-top: 0.4em;
}
.checkbox-trigger:checked + .menu-content ul {
  width: 200px;
  height: 200px;
  transition: width 0.7s ease 0.3s, height 0.3s ease;
}