Create a slide theme

This skill produces a theme bundle under themes/: two paired files that together describe a reusable visual identity.

1. themes/<id>.md — agent-facing documentation: palette, typography, layout, fixed Title/Footer/Eyebrow components, motion. This is what create-slide reads when an author picks the theme.
2. themes/<id>.demo.tsx — a runnable mini-slide (a normal slide module: export default Page[]) that demonstrates the theme on 2–3 pages. The dev UI's Themes panel loads this file and renders it as the theme's live preview.

Both files share the same stem so the runtime can pair them automatically.

A theme is distinct from a slide's design const. The theme markdown is authoring-time aesthetic direction (copied into a real slide's source by create-slide). The demo .tsx is a self-contained preview, not a real slide — it does not appear in the slides list. A per-slide const design: DesignSystem = { … } (declared at the top of slides/<id>/index.tsx) is the runtime tokens object the user can tweak from the Design panel. The markdown commits the direction; the per-slide design const makes the slide tweakable; the demo .tsx makes the theme previewable.

You only write files under themes/<id>.md and themes/<id>.demo.tsx. Never modify real slides or other configuration. The canvas / type-scale defaults that themes can override live in the slide-authoring skill — read it before writing the theme so your overrides are stated explicitly.

Step 1 — Identify the input source

A theme can be derived from any combination of three input shapes: