title: Javascript - How to zoom background-image
body: <p>I have div with fixed size and background-image in there. The image is much larger, than the container, but i have set background-position to show only chosen part of image. This works it's supposed to work.
  I need to make "zoom in" and "zoom out" buttons for  backgroundImage(in original ratio), but without changing size of it's container.</p>
  
  <p>Thank you for any advice.
  P.S.: I need pure javascript/css way.</p>