Function palette_root_css 

pub fn palette_root_css() -> String

Synthetic CSS source for the built-in lumen_core::palette::Palette light/dark theme: a base :root block from Palette::adwaita_light plus its differences wrapped in @media (prefers-color-scheme: dark) from Palette::adwaita_dark - the same light-first-with-dark-override shape every shipped skin file uses (core/runtime/src/skins/*.css).

Shared by both compile paths that build a combined stylesheet (lumen_runtime::run::loading::load_ir and lumenc::compile::compile_dir) so the two can never drift: each parses this once via its own front-end and prepends the result to its cascade, at the lowest precedence - beneath the always-on UA baseline, beneath any opted-in skin, and beneath the app’s own main.css. Sorted so the generated source (and therefore source_order) is deterministic across runs.

This is a snapshot, not a live source: nothing re-runs the cascade when a Palette value changes later. See lumen_core::palette’s module doc comment for why (parity with the precompiled-artifact run path, which ships with no CSS parser to re-run this against).