Struct CustomProp 

pub struct CustomProp {
    pub name: &'static str,
    pub owner: &'static str,
    pub default: &'static str,
    pub description: &'static str,
}

A CSS custom property a theme may set to reconfigure a component.

These are read by moss’s stylesheets as var(--moss-foo, <fallback>) and are deliberately never declared — that is exactly what makes them opt-in escape hatches rather than design tokens. A token has a value in :root and cascades site-wide; one of these has no value until a theme sets it, and it is set on a component or a scope to change that component.

The distinction matters because it is the whole theming API in practice. Audited 2026-08-03: the two most heavily customized moss sites (okagaki, 在場) overrode zero design tokens between them and set six of these. None was discoverable — not in moss describe --json, not in any published doc — so okagaki hand-fought the hero height caps that --moss-hero-max-height exists to lift, across three selectors and a 12-line comment.

Fields

name: &'static str

Property name including the leading dashes (e.g. "--moss-hero-max-height").

owner: &'static str

Class of the component whose rules read it, or a scope selector when no single class owns it (e.g. "body"). Free-form: this is documentation, not a foreign key.

default: &'static str

The fallback moss’s own CSS uses when the theme does not set it. Taken verbatim from the var() call site — never invented.

description: &'static str

What setting it does, and when you would want to.