custom theme inherits from. Any theme config options not defined in your theme
settings have their values set to those of the base theme. Valid values for
base are "light" and "dark".
For example, the following theme config defines a custom theme nearly identical
to the Streamlit Dark theme, but with a new primaryColor.
toml
[theme]
base="dark"
primaryColor="purple"
If base itself is omitted, it defaults to "light", so you can define a
custom theme that changes the font of the Streamlit Light theme to serif with
the following config
toml
[theme]
font="serif"
