<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$(":checked").wrap("<span style='background-color:red'>");
});
</script>
</head>
<body>
<form action="">
Name: <input type="text" name="user"><br>
I have a bike: <input type="checkbox" name="vehicle" value="Bike"><br>
I have a car: <input type="checkbox" name="vehicle" value="Car" checked="checked"><br>
I have an airplane: <input type="checkbox" name="vehicle" value="Airplane"><br>
<input type="submit">
</form>
<p>Note: We use jQuerys .wrap method to highlight the selected elements, because Firefox does not support background color on checkboxes.</p>
</body>
</html>