Adding an announcement banner

Furo makes it fairly straightforward to add a site-wide announcement (AKA top banner). The announcement is added to the top of all pages on the website.

This is done by setting announcement key in html_theme_options in your conf.py file. The value of this key is HTML, which is included as-is into the page.

html_theme_options = {
    "announcement": "<em>Important</em> announcement!",
}

The background and foreground of the announcement element are customisable, via the mechanisms described in Changing colors.