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In this guide, we provide examples of how Streamlit page elements are affected
by the various theme config options. For a more high-level overview of
Streamlit themes, see the Themes section of the
main concepts documentation.
Streamlit themes are defined using regular config options: a theme can be set
via command line flag when starting your app using streamlit run or by
defining it in the [theme] section of a .streamlit/config.toml file. For
more information on setting config options, please refer to the
Streamlit configuration documentation.
The following config options show the default Streamlit Light theme recreated
in the [theme] section of a .streamlit/config.toml file.
[theme]
primaryColor="#F63366"
backgroundColor="#FFFFFF"
secondaryBackgroundColor="#F0F2F6"
textColor="#262730"
font="sans serif"

Let's go through each of these options, providing screenshots to demonstrate
what parts of a Streamlit app they affect where needed.
primaryColor
primaryColor defines the accent color most often used throughout a Streamlit
app. A few examples of Streamlit widgets that use primaryColor include
st.checkbox, st.slider, and st.text_input (when focused).

starTipAny CSS color can be used as the value for primaryColor and the other color
options below. This means that theme colors can be specified in hex or with
browser-supported color names like "green", "yellow", and
"chartreuse". They can even be defined in the RGB and HSL formats!
backgroundColor
Defines the background color used in the main content area of your app.
secondaryBackgroundColor
This color is used where a second background color is needed for added
contrast. Most notably, it is the sidebar's background color. It is also used
as the background color for most interactive widgets.

textColor
This option controls the text color for most of your Streamlit app.
font
Selects the font used in your Streamlit app. Valid values are "sans serif",
"serif", and "monospace". This option defaults to "sans serif" if unset
or invalid.
Note that code blocks are always rendered using the monospace font regardless of
the font selected here.
base
An easy way to define custom themes that make small changes to one of the
preset Streamlit themes is to use the base option. Using base, the
Streamlit Light theme can be recreated as a custom theme by writing the
following:
[theme]
base="light"

The base option allows you to specify a preset Streamlit theme that your
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.
[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
[theme]
font="serif"
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