.close class is used to make a close button.aria-label attribute is set to close for screen readers devices.
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Bootstrap css helpers Example</title>
<link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<button type="button" class="close" aria-label="close">×</button><!--× is a HTML entity used to make a close button rather than using "X".-->
</div>
</body>
</html>
