Add this to your custom css:
.share-links > ul > li a {
border-radius: 50%;
display: block;
height: 20px;
padding: 5px;
text-align: center;
width: 20px;
line-height: 20px;
color: #fff;
}
To set each background color you will ned to use this css:
.share-links > ul > li a.product_share_facebook {
background-color: #3b5998;
}
For each icon change ‘facebook’ and the hex value
– Kyle