div{
background-color: green;
height: 50px;
width: 50px;
float: left;
margin: 40px;
}
.hover{
background-color: blue;
height: 60px;
width: 60px;
margin-right: 40px;
margin-top: 30px;
margin-left: 30px;
margin-bottom: 30px;
}
$(document).ready(function(){
$('div').hover(function(){
$(this).addClass('hover')
},
function(){
$(this).removeClass('hover')
}
)});
<html>
<head>
<link rel="stylesheet" type="text/css" href="style.css"/>
<script src="script.js"></script>
</head>
<body>
<div></div>
<div></div>
<div></div>
<div></div>
</body>
</html>