title: Show div while scrolling and change behavior
body: <p>I've already seen this sometimes, but I don't know how to realize it or how to search for it. That's why I would like to explain what it does:</p>
  <p>Let's say we got an image, an arrow and it points downwards and when you click on it, the page scrolls down. When I now scroll down and reach a specified point the arrow points upwards and brings me back to the top of the page.</p>
  <p>EDIT: I found an example. See the small arrow at the bottom and how it changes if you reach the end of the page. rorymcilroy.com</p>