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A workspace has one design.md: a few short paragraphs on how pages should look, and one ```css block. Every page in the workspace renders with that CSS, injected ahead of the page’s own styles, so pages use its classes and variables. Saving design.md restyles every page; there are no versions to manage, and a save that carries a stale fingerprint is refused rather than overwriting someone else’s edit. Admins edit design.md in Settings → Artifact theme, or click Copy setup for agent and paste the prompt into a coding agent open in their product’s code. The agent installs the sidecars-themes skill, reads the design from the codebase and saves design.md with write_theme.

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The format

  • At most one css block. It may use data: URLs only (no @import, no external url()), up to 64 KB — put the logo in as an SVG data URL.
  • The viewer sets data-theme="dark" on the page’s root in dark mode, so a :root[data-theme="dark"] block themes dark mode.
  • A css block that is refused still saves the file; pages keep the last good CSS until it is fixed.

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read_theme

Scope: documents:read · Kind: read-only · Annotations: readOnlyHint: true, destructiveHint: false, openWorldHint: false
Read the workspace’s design.md: prose that says how pages should look, and one css block every page renders with (css is that block as pages get it). Call it before creating or rewriting a page, then use its classes and variables and follow its prose; do not restate a colour or font it already sets. source: null when the workspace has none — pages then render with only their own styles. Pass the returned fingerprint to write_theme.

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Parameters

None.

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Returns

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string | null
The theme artifact’s id, or null when the workspace has no design.md.
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string
The web-app link the theme opens at.
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string | null
design.md, verbatim.
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string
Pass it to write_theme; a save carrying a stale one is refused.
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string
The css every page renders with.
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string
Present when the latest css block was refused; pages keep the last good css.

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write_theme

Scope: documents:write (step-up) · Kind: write, admin · Annotations: readOnlyHint: false, destructiveHint: true, idempotentHint: true, openWorldHint: false
Replace the workspace’s design.md with the whole file source, creating it if there is none. Admin only. Keep one css block; put the logo in it as an SVG data URL — the css may use data: URLs only, up to 64 KB. fingerprint is required: the one read_theme returned; if the file changed since, the save is refused with the current file — merge your change onto it and save again. Every page restyles as soon as it saves. A css block that is refused still saves the file and reports compile_error; pages keep the last good css until it is fixed.

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Parameters

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string
required
The whole design.md.
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string
required
The fingerprint read_theme returned. If design.md changed since, the save is refused with error: "design_changed", the current source and its fingerprint — merge and write again.

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Returns

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string
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string
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string
The saved file’s fingerprint, for the next save.
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string
Present when the css block was refused.