diff --git a/.github/workflows/check-links.yml b/.github/workflows/check-links.yml
index 8dd863e..91fa52c 100644
--- a/.github/workflows/check-links.yml
+++ b/.github/workflows/check-links.yml
@@ -18,6 +18,10 @@ env:
   # SHA256 of the above tarball, pinned at download time. Update alongside
   # LYCHEE_VERSION_TAG whenever the binary is upgraded.
   LYCHEE_SHA256: "1f4e0ef7f6554a6ed33dd7ac144fb2e1bbed98598e7af973042fc5cd43951c9a"
+  DART_SASS_VERSION: 1.99.0
+  # SHA256 of `dart-sass-${DART_SASS_VERSION}-linux-x64.tar.gz`, from the GitHub release.
+  # Update alongside DART_SASS_VERSION.
+  DART_SASS_SHA256: "f0a32ab99bc0a1eb62ea7140a056a1bca82d534390b7c3dba4f2016eb0077753"
   # Force Hugo to write its module cache where the cache step actually
   # restores from. Hugo's default on Linux is `~/.cache/hugo_cache`
   # (or `$TMPDIR/hugo_cache_$USER`), neither of which matches the
@@ -79,6 +83,21 @@ jobs:
           hugo-version: ${{ env.HUGO_VERSION }}
           extended: true
 
+      - name: Install Dart Sass
+        if: steps.docs.outputs.present == 'true'
+        run: |
+          archive="dart-sass-${DART_SASS_VERSION}-linux-x64.tar.gz"
+          curl -fsSLO "https://github.com/sass/dart-sass/releases/download/${DART_SASS_VERSION}/${archive}"
+          echo "${DART_SASS_SHA256}  ${archive}" | sha256sum --check --strict
+          tar -xzf "${archive}" -C "${RUNNER_TEMP}"
+          rm "${archive}"
+          echo "${RUNNER_TEMP}/dart-sass" >> "${GITHUB_PATH}"
+
+      # Hugo finds Dart Sass on `PATH`. `hugo env` lists it when it does.
+      - name: Check Dart Sass
+        if: steps.docs.outputs.present == 'true'
+        run: hugo env | grep 'github.com/sass/dart-sass'
+
       # `actions/setup-node@v4` ships with built-in npm caching that hashes
       # the lockfile and restores `~/.npm`. We use that instead of a
       # standalone `actions/cache@v4` block so there is only one source of
diff --git a/README.md b/README.md
index ddc12df..0478ea6 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,14 @@ are working as intended. It allows making changes more convenient for authors.
 2. [Go][go] `1.27.3` or newer (matches `docs/_preview/go.mod`).
 3. [Node.js][nodejs] `18+`.
 4. [Hugo Extended][hugo-quick-start] in version `v0.169.0` or higher.
+5. [Dart Sass][dart-sass] in version `1.99.0` or higher. On macOS, install it with Homebrew:
+
+   ```shell
+   brew install sass/sass/sass
+   ```
+
+   Hugo looks for the `sass` executable on `PATH`. When Hugo finds it,
+   `hugo env` lists `github.com/sass/dart-sass/...` entries.
 
 ## Configuration
 
@@ -202,6 +210,7 @@ the [`AUTHORING.md`][authoring-guide] file.
 [go]: https://go.dev/doc/install
 [nodejs]: https://nodejs.org/en/download/current
 [hugo-quick-start]: https://gohugo.io/getting-started/quick-start/#step-1-install-hugo
+[dart-sass]: https://gohugo.io/functions/css/sass/#dart-sass
 [site-commons]: https://github.com/SpineEventEngine/site-commons
 [embed-code]: https://github.com/SpineEventEngine/embed-code-go
 [authoring-guide]: https://github.com/SpineEventEngine/SpineEventEngine.github.io/blob/master/AUTHORING.md