How do you set Axis FontSize in Altair?

Question

I would like to increase the X-Axis (or Y-Axis for that matter) fontSize to 16 (or any value) in the following Altair graph. I could not find any example in the Altair documentation here: https://altair-viz.github.io/index.html . I am using Jupyter Lab for visualization. Intuitively alt.Axis should take FontSize argument

import altair as alt
from vega_datasets import data
cars = data.cars()

alt.Chart(cars).mark_point().encode(
    alt.X('Horsepower', axis=alt.Axis(title="HORSEPOWER")),
    alt.Y('Miles_per_Gallon', axis=alt.Axis(title="Miles Per Gallon")),
    color='Origin',
    shape='Origin'
)

Answer 1

One way you can do this is using the top-level chart configuration (think of it as a set of default chart properties). For example:

import altair as alt
from vega_datasets import data
cars = data.cars()

alt.Chart(cars).mark_point().encode(
    alt.X('Horsepower', axis=alt.Axis(title="HORSEPOWER")),
    alt.Y('Miles_per_Gallon', axis=alt.Axis(title="Miles Per Gallon")),
    color='Origin',
    shape='Origin'
).configure_axis(
    labelFontSize=20,
    titleFontSize=20
)

You can read more in Altair's Chart Configuration documentation.