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JavaScript

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HTML 

              
                <div class="nav__bar">
  <input type="checkbox" id="toggle" aria-hidden="true" />
  <label for="toggle" class="nav__icon" aria-hidden="true">
    Expand the menu
    <span class="nav__icon-line"></span>
    <span class="nav__icon-line"></span>
    <span class="nav__icon-line"></span>
  </label>
  <nav role="navigation" class="nav">
    <ul class="nav__items">
      <li class="nav__item"><a href="#">Item 1</a></li>
      <li class="nav__item"><a href="#">Item 2</a></li>
      <li class="nav__item"><a href="#">Item 3</a></li>
    </ul>
  </nav>
</div>

<h1>Pure CSS hamburger menu (accessible)</h1>
<p>
  Resize the browser to see the hamburger menu. This approach uses the checkbox hack to allow CSS to handle the hamburger toggle. The menu items will be accessible to screenreaders even when hidden.
</p>
<p>
  Inspired by <a href="https://codepen.io/bloom-dan/pen/vKdoar">https://codepen.io/bloom-dan/pen/vKdoar</a>
</p>
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CSS 

              
                // Variables
$breakpoint: 900px;
$green: #86973a;
$nav-height: 60px;

* {
  font-family: Helvetica, sans-serif;
  box-sizing: border-box;
}

.nav {

  &__bar {
    background-color: $green;
    padding-top: $nav-height;
    position: relative;

    @media (min-width: $breakpoint) {
      padding-top: 0;
    }
  }

  &__items {
    max-height: 1px; //0 would hide from screen readers
    overflow: hidden;
    list-style: none;
    margin: 0;
    padding: 0;
    transition: all 1s cubic-bezier(.325, 1, .22, 1);

    @media (min-width: $breakpoint) {
      max-height: none;
      text-align: center;
    }
  }

  &__item {
    padding: 0;
    margin: 0;
    background: #fff;

    @media (min-width: $breakpoint) {
      display: inline-block;
    }

    a {
      display: block;
      padding: 1em;
      margin: 0;
      border-bottom: 1px solid #fff;
      color: #fff;
      background: $green;
      font-size: 1.2rem;
      text-decoration: none;
      transition: opacity 0.5s ease;

      @media (min-width: $breakpoint) {
        display: inline-block;
        height: $nav-height;
        line-height: $nav-height;
        padding-top: 0;
        padding-bottom: 0;
        border: none;
      }

      &:link,
      &:visited {
        color: #fff;
      }

      &:hover,
      &:focus {
        text-decoration: none;
        opacity: 0.7;
      }
    }
  }

  &__icon {
    display: block;
    position: absolute;
    top: ($nav-height - 20px) / 2;
    right: 13px;
    height: 27px;
    width: 27px;
    cursor: pointer;
    text-indent: -9999px; //Hide the label
    transition: all 1s cubic-bezier(.19, 1, .22, 1);

    //Remove blinking cursor
    border: none;
    color: transparent;
    text-shadow: 0 0 0 gray;
    text-align: center;

    &:focus {
        outline: none;
    }

    @media (min-width: $breakpoint) {
      display: none;
    }
  }

  &__icon-line {
    position: absolute;
    display: block;
    background: #fff;
    width: 27px;
    height: .2rem;
    border-radius: .2rem;
    left: 0;
    text-indent: 0;
    transition: all .6s cubic-bezier(.5, .1, 0, 1.2);

    &:first-child {
      top: 0;
    }

    &:nth-child(2) {
      top: 8px;
    }

    &:nth-child(3) {
      top: 16px;
    }
  }
}

// Checkbox hack for toggling mobile menu
input[type=checkbox] {
  display: none;
  visibility: hidden;

  &:checked {

    ~ nav .nav__items {
      height: auto;
      max-height: 30rem;
      transition: all 2s cubic-bezier(.5, 1, .22, 1);
    }

    ~ label .nav__icon-line:first-child {
      top: 0px;
      width: 27px;
      transform: translateX(-8px) rotate(-45deg) translateY(12px);
    }

    ~ label .nav__icon-line:nth-child(2) {
      opacity: 0;
    }

    ~ label .nav__icon-line:nth-child(3) {
      top: 14px;
      width: 27px;
      transform: translateX(-5px) rotate(45deg) translateY(-8px);
    }
  }
}
!

JS
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