How to load serve static files in Flask

from flask import Flask, url_for, render_template

app = Flask(__name__,
            static_folder='static',
            template_folder='templates')

On file templates, you define them follow the example below:

<link rel="stylesheet" href="{{ url_for('static', filename='css/custom.css')}}">
<script src="{{ url_for('static', filename='js/site.js')}}"></script>