How to fit img into div circle ? (HTML/CSS)

I'm beginner in HTML/CSS.

I've created some div that looks like a circle. I want to put facebook image into that circle, but as a circle logo.

Click to see IMAGE

HTML

<div class="social" id="social1"> Facebook
  <a href="www.facebook.com">
    <img src="http://ift.tt/UJmW5i" width="106" height="106"/> 
     </a>
</div>

CSS

div {
     display: inline-block;
     margin-left: 55px;
     height: 100px;
     width: 100px;
     border-radius: 100%;
     border: 2px solid black;
     text-align:center;
   }

img {
     width: 100%;
     height : 100%;
     object-fit: contain;
    }