$(document).ready(function(){
$('body').keypress(function(){
$('#boxDiv').append('<div class="box"></div>');
});
});
<html>
<head>
<link rel="stylesheet" type="text/css" href="style.css"/>
<script src="script.js"></script>
</head>
<body>
<div id="boxDiv"></div>
</body>
</html>
.box{
background-color: red;
height: 50px;
width: 50px;
float: left;
}