title: CSS background blur on scroll
body: <p>I have fixed background image and upon scroll I want the image to go blur. I know how to do blur in css but do it at specific scroll position.</p>
  
  <p>Here is an example:
  <a href="https://medium.com/good-music/f160ba9e6c52">https://medium.com/good-music/f160ba9e6c52</a></p>
  
  <p>Any thoughts, examples, advice of snippets will be helpful.</p>
  
  <p>Thanks</p>