Bootstrap linked to web. Style not available offline

[RobertZickler]

The bootstrap stylesheets are linked to the web (output HTML line 10-12):

	<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
	<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
	<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

If no web connection is available the style is completely off:

The stylesheets should be linked and the files be available locally. At least as an build option.