<div class="slider">
  <div id="comparison">
    <figure>
      <div id="divisor"></div>
    </figure>
  </div>

  <div class="slider__menu">
    <button class="slider__menu-button button__min">Было</button>
    <input class="slider__menu-range" type="range" min="0" max="100" value="50" id="slider" oninput="moveDivisor()">
    <button class="slider__menu-button button__plus">Стало</button>
  </div>

</div>
</div>

div#comparison {
    width: 768px;
    height: 510px;
    margin: 0 auto;
    max-width: 650px;
    max-height: 517px;
    overflow: hidden;
    margin-bottom: 50px;
  }
  div#comparison figure {
    background-image: url(https://i.ibb.co/YbjFdpW/after-desktop.jpg);
    background-size: cover;
    background-repeat: no-repeat;
    position: relative;
    font-size: 0;
    width: 100%;
    height: 100%;
    margin: 0;
  }
  div#comparison figure > img {
    position: relative;
    width: 100%;
  }
  div#comparison figure div {
    background-image: url(https://i.ibb.co/5cZyrBb/before-desktop.jpg);
    background-size: cover;
    position: absolute;
    width: 50%;
    overflow: hidden;
    bottom: 0;
    height: 100%;
  }
  .slider__menu {
    width: 575px;
    margin: 0 auto;
  }
  .slider__menu-range {
    -webkit-appearance: none;
       -moz-appearance: none;
            appearance: none;
    position: relative;
    height: 6px;
    width: 425px;
    border-radius: 4px;
    background-color: #dcdcdc;
    margin-bottom: 100px;
  }
  .slider__menu-range:focus {
    outline: none;
  }
  .slider__menu-range:active {
    outline: none;
  }
  .slider__menu-range-webkit-::range-track {
    -webkit-appearance: none;
       -moz-appearance: none;
            appearance: none;
    height: 6px;
    width: 425px;
    background-color: #dcdcdc;
    position: relative;
    outline: none;
  }
  .slider__menu-range::active {
    border: none;
    outline: none;
  }
  .slider__menu-range::-webkit-slider-thumb {
    -webkit-appearance: none;
    position: relative;
    width: 32px;
    height: 32px;
    background-color: #fff;
    border: 2px solid #dcdcdc;
    border-radius: 50px;
    cursor: pointer;
    background-image: radial-gradient(at center center, #68b738, #68b738 4px, white 4px);
  }
  .slider__menu-range::-webkit-slider-thumb:hover {
    -webkit-box-shadow: 0px 3px 5px 0px rgba(0, 0, 0, 0.25);
            box-shadow: 0px 3px 5px 0px rgba(0, 0, 0, 0.25);
  }
  .slider__menu-range::-webkit-slider-thumb:active {
    border-color: #68b738;
  }
  .before-after__range::after {
    content: '';
    position: absolute;
    top: -1px;
    left: 209px;
    width: 8px;
    height: 8px;
    border-radius: 10px;
    background-color: #68b738;
  }
  .slider__menu-range::-moz-range-thumb {
    -moz-appearance: none;
    width: 32px;
    height: 32px;
    background: #fff;
    border: 1px solid #dcdcdc;
    border-radius: 50px;
  }
  .slider__menu-button {
    padding: 0;
    font-family: 'Oswald';
    background-color: transparent;
    border: none;
    font-size: 20px;
    font-weight: 400;
    border-bottom: 1px dotted #bebebe;
    cursor: pointer;
  }
  .slider__menu-button:hover {
    border-bottom: 1px solid #bebebe;
  }
  .slider__menu-button:active {
    border: none;
  }
  .slider__menu-button:focus {
    outline: none;
  }

var divisor = document.getElementById("divisor"),
        slider = 
        document.getElementById("slider");
        function moveDivisor() {
            divisor.style.width = slider.value+"%";
        }