<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="UTF-8">
<title>A Pen by Jose Cayo</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<p id="je" class="parrafo">Prueba final</p>
<script src='https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.0/jquery.min.js'></script>
<script src="js/index.js"></script>
</body>
</html>
/*Downloaded from https://www.codeseek.co/awkyo/a-pen-by-jose-cayo-gwovgB */
.parrafo {
background: red;
padding: 50px;
}
.par1 {
background: blue;
}
/*Downloaded from https://www.codeseek.co/awkyo/a-pen-by-jose-cayo-gwovgB */
$( "#je" ).click(function(){
$("#je").removeClass( "parrafo" ).addClass( "par1");
});