Using same port on dash

app2.py

#!/usr/bin/env python

import dash
import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Input, Output

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = dash.Dash(__name__, external_stylesheets=external_stylesheets)

app.layout = html.Div([

        'The dropdown menu is vanished',
        html.Br(),
        'Sample HTML'

])

app.run_server(debug=False, port= 8050, host= 'localhost')