The automatic supplied css file of Flask-bootstrap is like this:
<link href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
It is version 3. Is there any way to use bootstrap4 in flask-bootstrap? For now, I just change the css and js files to version 4 in my base template. But I am wondering if this will make some subtle problems.