Different theme configuration for some page within a website does impact the whole website

[cderv]

Reported once again for custom themed html page in website this time: https://forum.posit.co/t/directory-level-yaml-gets-applied-to-entire-quarto-website/188328/4

> quarto create project website test-subdir

Then add a subdir directory with subdir/index.qmd

{{< lipsum 1-2 >}}

and _metadata.yml

format:
  html:
    fontcolor: red

User is expecting to modify only the theme for this page.

In _quarto.yml

project:
  type: website

website:
  title: "example"
  navbar:
    left:
      - href: index.qmd
        text: Home
      - about.qmd
      - href: subdir/index.qmd
        text: Subdir

format:
  html:
    theme: cosmo
    css: styles.css
    toc: true

The results is that all Quarto theme information are merged in the same file moved in site_libs/bootstrap/bootstrap.min.css

So red will be set for $body-color

quarto-cli/src/format/html/format-html-scss.ts

Line 467 in 6b0728c

add(explicitVars, "body-color", metadata["fontcolor"]);

and applies to the whole site.

---

Some notes:

• @mcanouil remembers a discussion with @dragonstyle about this being by design because all pages in a single website should share the same theme. @dragonstyle if you pass around here, maybe you can share again the full story. thanks.

• If a single theme for all page is intended, we probably need to warn about or even prevent that a theme set one of the website page within the website is impacting the whole website. Really unexpected as a user.

• We have a variant of this problem of themes being merged in a single file for revealjs presentation. Presentations included in a website can only use one single theme because of this.

  • Different revealjs formats in a Quarto website don't work as expected #8383

[mcanouil]

Anyhow, I think allowing the theme to be changed across a website could be a nice/fancy enhancement but maybe not a small endeavour.

[cscheid]

My view is that if the behavior was intentional, then Quarto should disallow configurations that are scoped (like document and directory-level metadata) from creating settings that affect that entire project.

That happens to be a hard thing for Quarto to detect given the way metadata is stored and processed.

So this bug would be fixed in either of two ways, (both hard to do for different reasons):

• change the theming system so that different SCSS configurations generate different files that are separately managed and maintained
• change the metadata system so that "one-per-project" settings like themes cannot be set in "not-one-per-project" configuration files

[cscheid]

This should be fixed in https://github.com/quarto-dev/quarto-cli/releases/tag/v1.6.7.