Set width and height to empty link A tag in HTML

You are probably deal with link (A-tag) in HTML. But how we can set size if it is empty, i.e. with no content?
Here is example solution:

<!DOCTYPE html>
        a.link1, a.link2, a.link3 {display:block; 
            width: 100px; height: 100px;
            margin: 5px; float: left;}
        a.link1 {background-color: red;}
        a.link2 {background-color: green;}
        a.link3 {background-color: blue;}
        <a href="#1"></a>
        <a href="#2"></a>
        <a href="#3"></a>

As you can see, the key feature is adding display:block; to A-tag style.