Border around hyperlinked images

I’ve been struggling to get rid of a grey border and hover background color on some images with a hyperlink. I added these manually on one of my pages. One of the things I tried was adding below code to the Custom CSS at first, and later to the style.css but that didn’t work. Your advice would be much appreciated!

.contact_icons {
  border: 0;
  text-decoration: none;
  outline: none;
}

On the page I added the following:

<a href="" class="contact_icons"><img src=""></img></a>