After using pywebview to start the program with the full screen mode, it is no window border. Of course, there is no shutdown button, you can draw a button in the front page page, call the custom API method with the JS, refer to the problem on Stackoverflow:

https://stackoverflow.com/questions/65279193/how-to-close-pywebview-window-from-javascript-using-pywebview-api

Directly on the code, see the comment

import sqlite3
import webview
from flask import Flask, render_template

app = Flask(__name__)

conn = sqlite3.connect('data.db', check_same_thread=False)
c = conn.cursor()


@app.route('/')
def index():
    # Random drawn
    data = []
    cursor = c.execute('select * from tiku order by random() limit 2')
    # cursor = c.execute('select * from tiku where id = 62 or id = 67')
    for row in cursor:
        data.append({
            'id': row[0],
            'title': row[1],
            'answer': row[2]
        })
    return render_template('index.html', data=data)


# Define the API class definition to pass to the front-end JS, define internal properties _Window and set_window () methods to pass the Window objects in WebView you want to operate.
class Api:
    def __init__(self):
        self._window = None

    def set_window(self, window):
        self._window = window

    def quit(self):
        self._window.destroy()


def start_app():
    api = Api()
    window = webview.create_window(
        title='Tropical Procedure',
        url=app,
        confirm_close=True,
        fullscreen=True,
        js_api=api,
    )
    api.set_window(window)

    cn = {
        'global.quitConfirmation': u'confirm to close?'
    }

    webview.start(localization=cn, debug=True, gui='cef')


if __name__ == '__main__':
    # app.run(port=8000, debug=True)
    start_app()

Front-end call

// Call the PywebView's API
$("#exit").click(function () {
      pywebview.api.quit();
})