Fix CSS in static HTML export

[kylebarron]

Given default fonts, presumably css is not getting added to the static HTML page

[giswqs]

This issue might be relevant: opengeos/leafmap#594 (comment)

[kylebarron]

I don't think that's related. The standalone html export is working fine here; it's just missing our css.

[giswqs]

Never mind. The exported html doesn't work with Streamlit. I will look into it later.

[kiasari]

@giswqs Could you find a way to display the Map object in Streamlit?