<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Show video box example</title>
    <style>
      div {
        position: absolute;
        top: 50%;
        transform: translate(-50%,-50%);
        width: 480px;
        height: 380px;
        border-radius: 10px;
        background-color: #eee;
        background-image: linear-gradient(to bottom, rgba(0,0,0,0), rgba(0,0,0,0.1));
      }

      .hidden {
        left: -50%;
      }

      .showing {
        left: 50%;
      }

      div