add css style flask code example

Example 1: how to add css in flask app

<link rel= "stylesheet" type= "text/css" href= "{{ url_for('static',filename='styles/mainpage.css') }}">

Example 2: linking custom CSS in flask

{% block styles %}
{{super()}}
<link rel="stylesheet"
      href="{{url_for('.static', filename='mystyle.css')}}">
{% endblock %}