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Unknown theme name

theme
A theme name is not a built-in Bootswatch theme and is not a path to a .scss or .css file.

Q-14-2 — Unknown Theme Name

A theme name is not a built-in Bootswatch theme and is not a path to a .scss or .css file.

What this means

The theme: key (under format.html or a similar HTML-like format) accepts three shapes of value: the name of a built-in Bootswatch theme (cosmo, darkly, flatly, …), a path to a .scss or .css file in the project, or none to suppress the Bootstrap-derived default. This error fires when the value matches none of those — it is not a built-in name, and Quarto cannot find a file at the path.

Why this happens

Common causes:

  • A typo in a Bootswatch theme name (darkly is correct; darly is not).
  • A custom SCSS file referenced by relative path but the path is wrong, or the file lives outside the project root.
  • A theme name from a different framework (a TypeScript Quarto extension, a third-party theme pack) that has not been installed in this project.

How to fix

Pick a value Quarto can resolve:

  • A built-in Bootswatch name — the full list is in the Bootswatch documentation.
  • A path to a .scss or .css file inside the project.
  • theme: none to suppress Bootstrap entirely.

The error message includes a hint with the same options.