diff --git a/src/core/sass/brand.ts b/src/core/sass/brand.ts
index 480957b11e..d8121c6f9e 100644
--- a/src/core/sass/brand.ts
+++ b/src/core/sass/brand.ts
@@ -202,25 +202,37 @@ const brandColorLayer = (
   };
 };
 
+type BootstrapDefaultsConfig = {
+  uses?: string;
+  functions?: string;
+  defaults?: Record<string, Record<string, string | boolean | number | null>>;
+  mixins?: string;
+  rules?: string;
+};
+
 const brandDefaultsBootstrapLayer = (
   brand: Brand,
 ): SassLayer => {
   // Bootstrap Variables from brand.defaults.bootstrap
-  const brandBootstrap = brand?.data?.defaults?.bootstrap as unknown as Record<
-    string,
-    Record<string, string | boolean | number | null>
-  >;
+  const brandBootstrap = brand?.data?.defaults
+    ?.bootstrap as unknown as BootstrapDefaultsConfig;
 
   const bsVariables: string[] = [
     "/* Bootstrap variables from _brand.yml */",
-    '// quarto-scss-analysis-annotation { "action": "push", "origin": "_brand.yml defaults.bootstrap" }',
+    '// quarto-scss-analysis-annotation { "action": "push", "origin": "_brand.yml defaults.bootstrap.defaults" }',
   ];
-  for (const bsVar of Object.keys(brandBootstrap)) {
-    if (bsVar === "version") {
-      continue;
+  const bsDefaults = brandBootstrap.defaults || "";
+  if (typeof bsDefaults === "string") {
+    bsVariables.push(bsDefaults);
+  } else if (typeof bsDefaults === "object") {
+    for (const bsVar of Object.keys(bsDefaults)) {
+      bsVariables.push(`$${bsVar}: ${bsDefaults[bsVar]} !default;`);
     }
-    bsVariables.push(
-      `$${bsVar}: ${brandBootstrap[bsVar]} !default;`,
+  } else {
+    throw new Error(
+      "Invalid bootstrap defaults in _brand.yml or `brand`. " +
+        "`defaults.bootstrap.defaults` expects a string or a dictionary  " +
+        "mapping Sass variables to default values."
     );
   }
   bsVariables.push('// quarto-scss-analysis-annotation { "action": "pop" }');
@@ -253,20 +265,36 @@ const brandDefaultsBootstrapLayer = (
         continue;
       }
 
-      bsColors.push(
-        `$${colorKey}: ${brand.getColor(colorKey)} !default;`,
-      );
+      bsColors.push(`$${colorKey}: ${brand.getColor(colorKey)} !default;`);
     }
   }
 
   bsColors.push('// quarto-scss-analysis-annotation { "action": "pop" }');
 
+  const scssWithQuartoAnnotation = (
+    x: string | undefined,
+    origin: string
+  ): string => {
+    if (!x) {
+      return "";
+    }
+
+    return [
+      `// quarto-scss-analysis-annotation { "action": "push", "origin": "_brand.yml defaults.bootstrap.${origin}" }`,
+      x,
+      '// quarto-scss-analysis-annotation { "action": "pop" }',
+    ].join("\n");
+  };
+  
   return {
     defaults: bsColors.join("\n") + "\n" + bsVariables.join("\n"),
-    uses: "",
-    functions: "",
-    mixins: "",
-    rules: "",
+    uses: scssWithQuartoAnnotation(brandBootstrap.uses, "uses"),
+    functions: scssWithQuartoAnnotation(
+      brandBootstrap.functions,
+      "functions"
+    ),
+    mixins: scssWithQuartoAnnotation(brandBootstrap.mixins, "mixins"),
+    rules: scssWithQuartoAnnotation(brandBootstrap.rules, "rules"),
   };
 };