Hey @streamlitisawesome,
Thanks for sharing your question! It looks like that link actually goes to a Zoom meeting.
@mathcatsand has a good example of using a CSS file here (pasting below):
import streamlit as st
st.title('A Random App')
st.write('Look at the pretty waves')
with open('./files/wave.css') as f:
css = f.read()
st.markdown(f'<style>{css}</style>', unsafe_allow_html=True)