input: def create_flask_app() -> None:
      """
      Create a web application in Python using Flask that will take user input and generate an HTML page with the input.
      Example:
      >>> create_flask_app()
      No output expected except running the Flask application that takes user input and renders it on an HTML page.
      """
output:     
      from flask import Flask, request, render_template
  
      app = Flask(__name__)
  
      @app.route('/', methods=['GET', 'POST'])
      def index():
          if request.method == 'POST':
              user_input = request.form['user_input']
              return render_template('index.html', user_input=user_input)
          return render_template('index.html')
  
      if __name__ == '__main__':
          app.run(debug=True)
  