transition
<div>
<a href="javascript:;"></a>
</div>
a{
text-decoration: none;
width: 30px;
height: 30px;
background: #000;
border-radius: 50px;
position: absolute;
top:50%;left:50%;
margin-top:-15px;
margin-left: -15px;
transition: all 1s;
}
a:hover{
transform: scale(2);
}
div{
width:100px;
height:100px;
background:red;
position:relative;
}