CodePen Embed - CSS3 animated & responsive dropdown menu

<!--
  Animenu
  -------
  https://github.com/catalinred/animenu
  https://twitter.com/catalinred
-->

<nav class="animenu" role="navigation" aria-label="Menu">
  <button class="animenu__btn" type="button">
    <span class="animenu__btn__bar"></span>
    <span class="animenu__btn__bar"></span>
    <span class="animenu__btn__bar"></span>
  </button>

  <ul class="animenu__nav">
    <li><a href="#">Home</a></li>
    <li>
      <a href="#" class="animenu__nav__hasDropdown" aria-haspopup="true">Archive</a>
      <ul class="animenu__nav__dropdown" aria-label="submenu" role="menu">
        <li><a href="#" role="menuitem">Sub Item 1</a></li>
        <li><a href="#" role="menuitem">Sub Item 2</a></li>
        <li><a href="#" role="menuitem">Sub Item 3</a></li>
      </ul>
    </li>
    <li>
      <a href="#" class="animenu__nav__hasDropdown" aria-haspopup="true">Categories</a>
      <ul class="animenu__nav__dropdown" aria-label="submenu" role="menu">
        <li><a href="#" role="menuitem">Sub Item 1</a></li>
        <li><a href="#" role="menuitem">Sub Item 2</a></li>
        <li><a href="#" role="menuitem">Sub Item 3</a></li>
      </ul>
    </li>
    <li><a href="#">About</a></li>
    <li><a href="#">Contact</a></li>
  </ul>
</nav>

// Animenu
// -------
// https://github.com/catalinred/animenu
// https://twitter.com/catalinred

// Variables
$baseMenuBackground: #111;          // Base color theme
$secondaryMenuBackground: #0186ba;  // Secondary color (highlights, triangles...)
$gutter: 10px;                      // Base gutter

// Latest CSS box model 
*, *:after, *:before {
  box-sizing: border-box; 
}

// The classic hamburger icon
// <button class="animenu__btn">
//   <span class="animenu__btn__bar"></span>
//   <span class="animenu__btn__bar"></span>
//   <span class="animenu__btn__bar"></span>
// </button>
.animenu__btn {
  display: none;
  cursor: pointer;
  background-color: $baseMenuBackground;
  border: 0; 
  padding: 10px;
  height: 40px;
  width: 40px;

  &:hover {
    background-color: $secondaryMenuBackground;
  }
}

.animenu__btn__bar {
  display: block;
  width: 20px; height: 2px;
  background-color: #fff;    
  transition: .15s cubic-bezier(0.75, -0.55, 0.25, 1.55);

  &+.animenu__btn__bar {
    margin-top: 4px;
  }  
}

.animenu__btn--active {
  .animenu__btn__bar {
    margin: 0;
    position: absolute;

    &:nth-child(1) {
      transform: rotate(45deg);
    }

    &:nth-child(2) {
      opacity: 0;
    }

    &:nth-child(3) {
      transform: rotate(-45deg);
    }        
  }
}

// Clear some defaults
.animenu {
  display: block;
  ul {
    padding: 0;
    list-style: none;    
    font: 0 -apple-system,
            BlinkMacSystemFont,   
            "Segoe UI",          
            "Roboto",
            "Helvetica Neue", Arial, sans-serif,
            "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";    
  }

  li, a {
    display: inline-block;
    font-size: 15px;
  }

  a {
    color: lighten($baseMenuBackground, 60%);
    text-decoration: none;
  }
}

// First level -> main menu items
// <nav class="animenu">
//    <ul class="animenu__nav">
//    ...
//    </ul>
//  </nav>
.animenu__nav {
  background-color: $baseMenuBackground;        

  > li {
    position: relative;
    border-right: 1px solid lighten($baseMenuBackground, 20%);

    > a {
      padding: $gutter 3 * $gutter;
      text-transform: uppercase; 
    }    

    &:hover {
      > ul {
        opacity: 1;
        visibility: visible;
        margin: 0;        
      }

      > a {
        color: #fff;
      }
    }

    // Duplicate stuff due to 
    // https://www.w3.org/TR/2018/PR-selectors-3-20180911/#grouping
    &:focus-within {
      > ul {
        opacity: 1;
        visibility: visible;
        margin: 0;        
      }
      
      > a {
        color: #fff;
      }
    }    
  }

  &__hasDropdown:before { 
    content:""; 
    position: absolute;
    border: 4px solid transparent;
    border-bottom: 0; 
    border-top-color: currentColor;
    top: 50%;
    margin-top: -2px;
    right: 10px;  
  }   
}

// Second level
// <nav class="animenu">
//    <ul class="animenu__nav">
//      <li>
//        <ul class="animenu__nav__dropdown"></ul>
//      </li>
//    </ul>
//  </nav>
.animenu__nav__dropdown {
  min-width: 100%;
  position: absolute;
  top: 100%; left: 0;
  z-index: 1;   
  opacity: 0;
  visibility: hidden;
  margin: 2 * $gutter 0 0 0;
  background-color: lighten($baseMenuBackground, 15%);    
  transition: margin .15s, opacity .15s;

  > li {
    width: 100%;
    border-bottom: 1px solid lighten($baseMenuBackground, 25%);

    &:first-child > a:after {
      content: '';
      position: absolute;
      height: 0; width: 0;
      left: 1em;
      top: -6px;
      border: 6px solid transparent;
      border-top: 0;
      border-bottom-color: inherit;
    }

    &:last-child {
      border: 0;
    }
  }

  a {
    padding: $gutter;
    width: 100%;
    border-color: lighten($baseMenuBackground, 15%);

    &:hover {
      background-color: $secondaryMenuBackground;
      border-color: $secondaryMenuBackground;
      color: #fff;
    }

    // Duplicate stuff due to 
    // https://www.w3.org/TR/2018/PR-selectors-3-20180911/#grouping  
    &:focus-within {
      background-color: $secondaryMenuBackground;
      border-color: $secondaryMenuBackground;
      color: #fff;
    }    
  }
}

// The main breakpoint is 767px
// Adjust the first and second levels display
@media screen and (max-width: 767px) {
  .animenu__btn {
    display: inline-block;
  }

  .animenu__nav,
  .animenu__nav__dropdown {
    display: none;
  }

  // First level -> main menu items
  // <nav class="animenu">
  //    <ul class="animenu__nav">
  //    ...
  //    </ul>
  //  </nav>    
  .animenu__nav {
    margin: $gutter 0;

    > li {
      width: 100%;
      border-right: 0;
      border-bottom: 1px solid lighten($baseMenuBackground, 25%);

      &:last-child {
        border: 0; 
      }

      &:first-child > a:after {
        content: '';
        position: absolute;
        height: 0; width: 0;
        left: 1em;
        top: -6px;
        border: 6px solid transparent;
        border-top: 0;
        border-bottom-color: inherit;
      }

      > a {
        width: 100%;
        padding: $gutter;
        border-color: $baseMenuBackground;
        position: relative; //dropdown caret
      }
    }

    a:hover {
      background-color: $secondaryMenuBackground;
      border-color: $secondaryMenuBackground;
      color: #fff;      
    }
  }

  // Second level
  // <nav class="animenu">
  //    <ul class="animenu__nav">
  //      <li>
  //        <ul class="animenu__nav__dropdown"></ul>
  //      </li>
  //    </ul>
  //  </nav>              
  .animenu__nav__dropdown {
    position: static;
    background-color: lighten($baseMenuBackground, 15%);
    margin: 0;
    transition: none;
    visibility: visible;
    opacity: 1;     

    > li:first-child > a:after {
      content: none;
    }

    a {
      padding-left: 2 * $gutter;
      width: 100%;
    }           
  }
}

// Expanding the animenu
// <nav class="animenu">
//    <ul class="animenu__nav animenu__nav--active">
//      <li>
//        <ul class="animenu__nav__dropdown"></ul>
//      </li>
//    </ul>
//  </nav>
.animenu__nav--active {
  display: block !important;

  & .animenu__nav__dropdown {
    display: block;
  }
}

View Compiled

// Animenu
// -------
// https://github.com/catalinred/animenu
// https://twitter.com/catalinred

// ES6
// a.k.a unicorns everywhere 🙂
(() => {
  let $ = el => document.querySelector(el);
  
  $(".animenu__btn").addEventListener("click", function(){
    this.classList.toggle("animenu__btn--active")
    $(".animenu__nav").classList.toggle("animenu__nav--active")
  });
})()

// ---

// IE 10
// https://caniuse.com/#search=classlist

// (function(){
//   var $ = function(el) { 
//     return document.querySelector(el); 
//   }
  
//   $('.animenu__btn').addEventListener('click', function() {
//     this.classList.toggle("animenu__btn--active")
//     $('.animenu__nav').classList.toggle("animenu__nav--active")
//   });
// })();

// ---

// IE9 / IE8
// https://caniuse.com/#search=querySelector

// (function(){
//   var animenuToggle = document.querySelector('.animenu__btn'),
//       animenuNav    = document.querySelector('.animenu__nav'),
//       hasClass = function( elem, className ) {
//         return new RegExp( ' ' + className + ' ' ).test( ' ' + elem.className + ' ' );
//       },
//       toggleClass = function( elem, className ) {
//         var newClass = ' ' + elem.className.replace( /[\t\r\n]/g, ' ' ) + ' ';
//         if( hasClass(elem, className ) ) {
//           while( newClass.indexOf( ' ' + className + ' ' ) >= 0 ) {
//             newClass = newClass.replace( ' ' + className + ' ' , ' ' );
//           }
//           elem.className = newClass.replace( /^\s+|\s+$/g, '' );
//         } else {
//           elem.className += ' ' + className;
//         }
//       },           
//       animenuToggleNav =  function (){        
//         toggleClass(animenuToggle, "animenu__btn--active");
//         toggleClass(animenuNav, "animenu__nav--active");        
//       }

//   if (!animenuToggle.addEventListener) {
//     animenuToggle.attachEvent("onclick", animenuToggleNav);
//   }
//   else {
//     animenuToggle.addEventListener('click', animenuToggleNav);
//   }
// })()

This Pen is owned by Catalin Rosu on CodePen.

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