title: JavaScript, html5: how to dynamically create a Vignette effect?
body: <p>So what I need is simple: user presses something, user sees Vignette effect on new div on top of all page (with page size) alike  <img src="https://i.stack.imgur.com/LCvmX.jpg" alt="chrome set up page"></p>
  
  <p>Is it possible with some html5 canvas art? And how to do such thing?</p>