I added a custom theme using a config.toml file in the .streamlit folder. I can access the theme in my localhost and everything work as intended but when I deploy my app using Streamlit cloud the new theme never appears.
.streamlit/config.toml
[theme]
base="dark"
backgroundColor="#577887"
Everything went fine. I just had to reboot my app for a second time since it had problems fetching from GitHub.