Check out this cool upload button animation designed by Eva Lettner. When you click on the upload button, the circular space will start to fill up and the upload icon will transform into a tick icon. Simultaneously the upload button will transform into a reset button. And when you click on the reset button everything will reverse. The circular space will get emptied, the tick icon and the reset button will change into upload option.
If you are having trouble with the pen, try the archived copy on GitHub