#let css-list = state("css-list", ())

/// Add string `css` to `css-list` if not already present
#let add-css(css) = context {
  css-list.update(x => if css in x { x } else { x + (css,) })
}

/// Concatenate all css found in css-list at the end of the document
#let get-css() = context {
  css-list.final().join("\n\n")
}

#let html_show(body) = {
  show raw.where(lang: "raw-css"): it => add-css(it.text)
  body
}