.container {
  max-width: 800px;
  margin:0 auto;
  width: 100%; 
   font-family: Verdana, Arial, Helvetica, sans-serif;   
}
  * {
  box-sizing: border-box;
}
.img-comp-group {
  margin: 20px 0px;
  position: relative;
  min-height: 450px;
}
.img-comp-container {

}
.img-comp-img {
  position: absolute;
  width: auto;
  height: auto;
  overflow: hidden;
}
.img-comp-img img {
  display: block;
  vertical-align: middle;
}
.img-comp-slider {
  position: absolute;
  z-index: 9;
  cursor: ew-resize;
  width: 30px;
  height: 80px;
  background-color: #2196f3;
  opacity: 0.9;
  border-radius: 8px;
}
.separator {
  height: 13em;
}

function initComparisons() {
  var x, i;
  x = document.getElementsByClassName("img-comp-overlay");
  for (i = 0; i < x.length; i++) {
    compareImages(x[i]);
  }
  function compareImages(img) {
    var slider, img, clicked = 0, w, h;
    w = img.offsetWidth;
    h = img.offsetHeight;
    img.style.width = (w / 2) + "px";
    slider = document.createElement("DIV");
    slider.setAttribute("class", "img-comp-slider");
    img.parentElement.insertBefore(slider, img);
    slider.style.top = (h / 2) - (slider.offsetHeight / 2) + "px";
    slider.style.left = (w / 2) - (slider.offsetWidth / 2) + "px";
    slider.addEventListener("mousedown", slideReady);
    window.addEventListener("mouseup", slideFinish);
    slider.addEventListener("touchstart", slideReady);
    window.addEventListener("touchstop", slideFinish);
    function slideReady(e) {
      e.preventDefault();
      clicked = 1;
      window.addEventListener("mousemove", slideMove);
      window.addEventListener("touchmove", slideMove);
    }
    function slideFinish() {
      clicked = 0;
    }
    function slideMove(e) {
      var pos;
      if (clicked == 0) return false;
      pos = getCursorPos(e)
      if (pos < 0) pos = 0;
      if (pos > w) pos = w;
      slide(pos);
    }
    function getCursorPos(e) {
      var a, x = 0;
      e = e || window.event;
      a = img.getBoundingClientRect();
      x = e.pageX - a.left;
  
      x = x - window.pageXOffset;
      return x;
    }
    function slide(x) {
      img.style.width = x + "px";
      slider.style.left = img.offsetWidth - (slider.offsetWidth / 2) + "px";
    }
  }
}
initComparisons();