index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="stylesheet" href="app.css" />
    <title>Before and After Image Slider</title>
  </head>
  <body>
    <h1>Before and After Image Slider</h1>
    <form>
      Add "before" image:
      <input type="file" accept="image/*" name="" id="before-selector" onchange="updateImage()"/>
      <br />
      Add "after" image:
      <input type="file" accept="image/*" name="" id="after-selector" onchange="updateImage()"/>
    </form>
    <div class="image-container">
      <input type="range" name="" id="" min="0" max="100" value="50" tabindex="-1"/>
      <div class="image-after"></div>
      <div class="image-before"></div>
    </div>
    <script src="index.js"></script>
  </body>
</html>