x
 
<!Doctype html>
<html>
<style>
#container {
  width: 400px;
  height: 400px;
  position: relative;
  background: yellow;
}
#animate {
  width: 50px;
  height: 50px;
  position: absolute;
  background: red;
}
</style>
<body>
<h2>My First JavaScript Animation</h2>
<div id="container">
<div id="animate"></div>
</div>
</body>
</html>