toggle-button.css

<a href="javascript:void(0);" class="toggle-btn hidden-lg"><span></span></a>

.toggle-btn {
  display: block;
  width: 28px;
  height: 28px;
  margin-top: 14px;
}
.toggle-btn span::after, .toggle-btn span::before {
  content: "";
  position: absolute;
  left: 0;
  top: 9px;
}
.toggle-btn span::after {
  top: 18px;
}
.toggle-btn span {
  position: relative;
  display: block;
}
.toggle-btn span, .toggle-btn span::after, .toggle-btn span::before {
  width: 100%;
  height: 2px;
  background-color: #fff;
  transition: all 0.3s;
  backface-visibility: hidden;
  border-radius: 2px;
}
.toggle-btn.on span {
  background-color: transparent;
}
.toggle-btn.on span::before {
  transform: rotate(45deg) translate(-1px, 0px);
}
.toggle-btn.on span::after {
  transform: rotate(-45deg) translate(6px, -7px);
}

// Scripts
$('.toggle-btn').on('click', function() {
  $(this).toggleClass('on');
  $('.main-menu').slideToggle();
  return false;
});

$(window).resize(function(){
  if($(window).width() > '768')   {
    $('.main-menu').removeAttr('style');
    $('.toggle-btn').removeClass('on');
  }
});