title: HTML/CSS - create alpha mask over image
body: <p>I'd like to create an effect in a site I’m building where an image is masked by an overlay. The overlay should create a “fade out” effect — I don’t actually want anything animated, but the overlay should make the image look as if it’s fading to the background colour at the edges.</p>
  
  <p>Something like this: <a href="https://imgur.com/fqtc9.png" rel="noreferrer">http://imgur.com/fqtc9.png</a></p>
  
  <p>I prefer to do this with CSS/HTML/JS - not images. Any thoughts on where to start? Thanks.</p>