body
  .hamburger
    .hamburger-button
      .icon-opened
        .bar
        .bar
        .bar
    .hamburger-button.hamburger-button-back
      .icon-closed
        .bar
        .bar

body {
  background: linear-gradient(to right, #8e9eab, #eef2f3);
  display: flex;
  align-items: center;
  align-content: center;
  height: 100vh;
  width: 100vw;
  text-align: center;
  margin: 0;
}

.hamburger {
  margin: 0 auto;
  width: 6rem;
  height: 6rem;
  transition: all 300ms ease-in;
  transform-style: preserve-3d;
  
  &-button {
    border-radius: 100px;
    display: inline-block;
    cursor: pointer;
    background: linear-gradient(to right, #485563, #29323c);
    // the padding along with the inner wrap adds up to 6rem*6rem circle
    padding: 1.85rem 1.5rem;
    position: absolute;
    top: 0;
    left: 0;
    backface-visibility: hidden;
    &-back {
      transform: rotateY(180deg);
    }
  }
  
  .icon-opened {
    height: 2.3rem;
    width: 3rem;
    position: relative;
    .bar {
      border-bottom: 0.33rem solid white;
      position: absolute;
      display: block;
      width: 100%;
      &:first-of-type {
        top: 0;
      }
      &:nth-of-type(2) {
        top: 1rem;
      }
      &:nth-of-type(3) {
        top: 2rem;
      }
    }
  }


  .icon-closed {
    height: 2.3rem;
    width: 3rem;
    position: relative;
    backface-visibility: hidden;
    .bar {
      border-bottom: 0.33rem solid white;
      position: absolute;
      display: block;
      width: 100%;
      &:first-of-type {
        top: 1em;
        transform: rotate(45deg);
      }
      &:nth-of-type(2) {
        top: 1em;
        transform: rotate(-45deg);
      } 
    }
  }
}

.hamburger.opened {
  transform: rotateY(180deg);
} 

const hamburger = document.querySelector('.hamburger');
hamburger.addEventListener('click', function(){
  hamburger.classList.toggle('opened');
});