RESPONSIVE before/after slider forked

HTML

<script src="https://zurb.com/playground/uploads/upload/upload/92/jquery.twentytwenty.js"></script>
<script src="https://zurb.com/playground/uploads/upload/upload/91/jquery.event.move.js"></script>
<div id='container1' class='twentytwenty-container'>
  <img src="https://i.imgur.com/KhMHxI5.png" width= "50%">
  <img src="https://i.imgur.com/CPjc0Ka.png" width= "50%">
</div>

CSS

.twentytwenty-handle:before, .twentytwenty-handle:after {
  content: " ";
  display: block;
  width: 3px;
  background: white;
  height: 9999px;
  position: absolute;
  left: 50%;
  margin-left: -1.5px;
  z-index: 30;
  -webkit-box-shadow: 0px 0px 12px rgba(51, 51, 51, 0.5);
  -moz-box-shadow: 0px 0px 12px rgba(51, 51, 51, 0.5);
  box-shadow: 0px 0px 12px rgba(51, 51, 51, 0.5); }

.twentytwenty-before-label, .twentytwenty-after-label, .twentytwenty-overlay {
  position: absolute;
  top: 0;
  width: 100%;
  height: 100%; }

.twentytwenty-before-label, .twentytwenty-after-label, .twentytwenty-overlay {
  -webkit-transition-duration: 0.5s;
  -moz-transition-duration: 0.5s;
  transition-duration: 0.5s; }

.twentytwenty-before-label, .twentytwenty-after-label {
  -webkit-transition-property: opacity;
  -moz-transition-property: opacity;
  transition-property: opacity; }

.twentytwenty-before-label:before, .twentytwenty-after-label:before {
  color: white;
  font-size: 13px;
  letter-spacing: 0.1em; }

.twentytwenty-before-label:before, .twentytwenty-after-label:before {
  background: rgba(255, 255, 255, 0.2);
  position: absolute;
  top: 50%;
  margin-top: -19px;
  line-height: 38px;
  padding: 0 20px;
  -webkit-border-radius: 2px;
  -moz-border-radius: 2px;
  border-radius: 2px; }

.twentytwenty-left-arrow, .twentytwenty-right-arrow {
  width: 0;
  height: 0;
  border: 6px inset transparent;
  position: absolute;
  top: 50%;
  margin-top: -6px; }

.twentytwenty-container {
  -webkit-box-sizing: content-box;
  -moz-box-sizing: content-box;
  box-sizing: content-box;
  overflow: hidden;
  position: relative;
  -webkit-user-select: none;
  -moz-user-select: none; }
  .twentytwenty-container img {
    position: absolute;
    top: 0;
    display: block; }
  .twentytwenty-container.active .twentytwenty-overlay, .twentytwenty-container.active :hover.twentytwenty-overlay {
    background: rgba(0, 0, 0, 0); }
    .twentytwenty-container.active .twentytwenty-overlay...

JavaScript

$(window).load(function() {
  $("#container1").twentytwenty();
});

$(document).ready(function() {
  $("#container1").twentytwenty();
    $(".openthis").click(function() {
    $("#content").show("slow");
  });
});