Please fix the following code base for a flask app. Here is index.html
<!DOCTYPE html>

<html lang="en">
    <head>
        <link href="https://fonts.googleapis.com/css2?family=Montserrat:wght@500&display=swap" rel="stylesheet">
        <link href="/static/styles.css" rel="stylesheet">
        <title>Birthdays</title>
    </head>
    <body>
        <div class="header">
            <h1>Birthdays</h1>
        </div>
        <div class="container">
            <div class="section">

                <h2>Add a Birthday</h2>
                <!-- TODO: Create a form for users to submit a name, a month, and a day -->
                <form action="/" method="post">
                    <label for="name">First and Last Name</label><br>
                    <input type="text" id="name" name="name"><br>
                    <label for="month">In what month were you born?</label><br>
                    <input type="text" id="month" name="month"><br>
                    <label for="day">What day were you born?</label><br>
                    <input type="text" id="day" name="day"><br><br>
                    <input type="submit" value="Submit">
                </form>
            </div>

            <div class="section">

                <h2>All Birthdays</h2>
                <table>
                    <thead>
                        <tr>
                            <th>Name</th>
                            <th>Day</th>
                            <th>Month</th>
                        </tr>
                    </thead>
                    <tbody>
                        <!-- TODO: Loop through the database entries to display them in this table -->

                        {% for registrant in registrants %}

                        <tr>
                            <td>{{ registrant.name }}</td>
                            <td>{{ registrant.sport }}</td>
                            <td>
                                <form action="/deregister" method="post">
                                    <input name="id" type="hidden" value="{{ registrant.id }}">
                                    <button type="submit">Deregister</button>
                                </form>
                            </td>
                        </tr>
                        {% endfor %}
                    </tbody>
                </table>
            </div>
        </div>
    </body>
</html>

And here is app.py
import os

from cs50 import SQL
from flask import Flask, flash, jsonify, redirect, render_template, request, session

# Configure application
app = Flask(__name__)

# Ensure templates are auto-reloaded
app.config["TEMPLATES_AUTO_RELOAD"] = True

# Configure CS50 Library to use SQLite database
db = SQL("sqlite:///birthdays.db")


@app.after_request
def after_request(response):
    """Ensure responses aren't cached"""
    response.headers["Cache-Control"] = "no-cache, no-store, must-revflaskdate"
    response.headers["Expires"] = 0
    response.headers["Pragma"] = "no-cache"
    return response


# @app.route("/deregister", methods=["POST"])
# def deregister():

#     # Forget registrant
#     id = request.form.get("id")
#     if id:
#         db.execute("DELETE FROM registrants WHERE id = ?", id)
#     return redirect("/registrants")




@app.route("/", methods=["GET", "POST"])
def index():
    if request.method == "POST":

        # TODO: Add the user's entry into the database

        return redirect("/")

    else:

        # TODO: Display the entries in the database on index.html

        return render_template("index.html")