Add halo to image when hover

Question

First time posting. I have the following shortcode in my stylesheet for creating images in circles

.make-circle {
  -webkit-border-radius: 50%;
  -moz-border-radius: 50%;
  border-radius: 50%; 

}

If I want to add a 'halo' shadow on hover how would I go about adding this in here? I was thinking about making a new class and then adding it to the img tag but I think this would clash with the above shortcode? This is the code for referencing the above:

<img class="make-circle" src="#">

Any help much appreciated