Use a hover
pseudo-class like this:
#link-id{
height:300px;
width:300px;
font-size:20px;
background:red;
display:block;
transition:0.5s ease;
}
#link-id:hover{ /*or .link-class if targeting by class*/
font-size:30px;
background:blue;
cursor:poitner;
text-align:center;
}