title: Highlight div corners for cropping tool
body: <p>I am working on a cropping tool where I need to highlight corners of a div with strong black like so: <br> 
  (Any kind of highlight on the corner will be fine, the one shown in the image is overdoing it). <br><a href="https://i.stack.imgur.com/fdYcE.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fdYcE.jpg" alt="enter image description here"></a>
   <br> Such a highlight would indicate diagonal cropping as opposed to linear cropping on the edges. How can I accomplish this using CSS or javascript. (Borders can be easily highlighted, but corners?)<br> <br>
  Thanks!</p>