title: How to change button background as a progress?
body: <p>I'm trying to change the background of a button as a "loading" while it's pressed, but I'm not sure how to make. </p>
  
  <p>First I tried to use a progress bar but, what I want is to load the background progressively if the button is pressed or revert it if the button is released.</p>
  
  <p>Thanks in advance for any idea.</p>