Hey @Amine_YK,
First, welcome to the Streamlit community!

To troubleshoot can you check:
- You have
Streamlit --version0.79 or higher? - That you have created a secret or hidden streamlit directory in the same folder your app is in
.streamlit/ - that your config file is named properly
config.toml - that
[theme]is the first entry in this file and is all lower case
If after checking this, everything is correct and your still having issues, I would recommend creating a new question. This should outline your issue and have a minimum working example of your code (or ideally a link to a GitHub repo)
You can check out the guidelines for asking questions that will help others help you here: Welcome ! Some suggestions for your first Streamlit question
Happy Streamlit-ing!
Marisa