Streamlit is not working in localhost

My code is app.py

import streamlit as st
st.write("hello")

run this code with streamlit run app.py

You can now view your Streamlit app in your browser.

Network URL: http://XXX.XXX.XXX.X:8501 External URL: http://XX.X.XXX.XX:8501

I follow the https://XXX/jupyterlab/default/proxy/8501 but tis is not working for me