Vega-lite charts do not show titles in dark mode

[jrieke]

Summary

Titles of Vega-Lite charts are not showing up in dark mode.

Steps to reproduce

Originally reported by @tvst:

There are actually titles right above those 2 charts, but you can’t see them because they’re black-on-black. I think our Vega-Lite theme is missing some property. Maybe need to add titleColor to header?

The screenshot above is from the Plost example app. Here’s a simple way to repro locally:

pip install plost

then

import plost

plost.bar_chart(
    data=datasets['stocks'],
    bar='company',
    value=['q2', 'q3'],
    group='value',
    color='company',
    legend=None,
)

Is this a regression?

That is, did this use to work the way you expected in the past?
idk

Debug info

• Streamlit version: (get it with $ streamlit version)
• Python version: (get it with $ python --version)
• Using Conda? PipEnv? PyEnv? Pex?
• OS version:
• Browser version:

Additional information

If needed, add any other context about the problem here. For example, did this bug come from https://discuss.streamlit.io or another site? Link the original source here!