diff --git a/news/changelog-1.9.md b/news/changelog-1.9.md
index 0f61d281a9c..70b02eedd29 100644
--- a/news/changelog-1.9.md
+++ b/news/changelog-1.9.md
@@ -50,6 +50,7 @@ All changes included in 1.9:
 - ([#13825](https://github.com/quarto-dev/quarto-cli/issues/13825)): Fix `column: margin` not working with `renderings: [light, dark]` option. Column classes are now preserved when applying theme classes to cell outputs.
 - ([#13883](https://github.com/quarto-dev/quarto-cli/issues/13883)): Fix unequal top/bottom spacing in simple untitled callouts.
 - ([#13900](https://github.com/quarto-dev/quarto-cli/issues/13900)): Warn when `renderings` cell option contains duplicate names. Previously, duplicate names like `[dark, light, dark, light]` would silently use only the last output for each name.
+- ([#14065](https://github.com/quarto-dev/quarto-cli/issues/14065)): Fix `SCSSParsingError` when custom SCSS themes contain non-ASCII characters in selectors (e.g., `#présentation`).
 
 ### `typst`
 
diff --git a/src/core/sass/add-css-vars.ts b/src/core/sass/add-css-vars.ts
index 3edcd99be8b..7d762bf0862 100644
--- a/src/core/sass/add-css-vars.ts
+++ b/src/core/sass/add-css-vars.ts
@@ -16,6 +16,16 @@ import { getVariableDependencies } from "./analyzer/get-dependencies.ts";
 
 const { getSassAst } = makeParserModule(parse);
 
+// Reverse the _u<hex>_ encoding applied in parse.ts so that
+// variable names emitted into the CSS vars block match the
+// original SCSS source that Dart Sass compiles against.
+// Non-ASCII codepoints are valid in CSS custom property names since they
+// follow the <ident> production (see spec references in parse.ts).
+const decodeScssName = (name: string) =>
+  name.replace(/_u([0-9a-f]+)_/g, (_, hex: string) =>
+    String.fromCodePoint(parseInt(hex, 16))
+  );
+
 export class SCSSParsingError extends Error {
   constructor(message: string) {
     super(`SCSS Parsing Error: ${message}`);
@@ -38,7 +48,8 @@ export const cssVarsBlock = (scssSource: string) => {
   for (const [dep, _] of deps) {
     const decl = ast.get(dep);
     if (decl.valueType === "color") {
-      output.push(`--quarto-scss-export-${dep}: #{$${dep}};`);
+      const originalName = decodeScssName(dep);
+      output.push(`--quarto-scss-export-${originalName}: #{$${originalName}};`);
     }
   }
   output.push("}");
diff --git a/src/core/sass/analyzer/parse.ts b/src/core/sass/analyzer/parse.ts
index 5e9794a34a8..a2f73206c80 100644
--- a/src/core/sass/analyzer/parse.ts
+++ b/src/core/sass/analyzer/parse.ts
@@ -41,6 +41,21 @@ export const makeParserModule = (
         "$1: $2",
       );
 
+      // scss-parser's tokenizer only handles ASCII identifier characters.
+      // Non-ASCII codepoints are valid in both CSS and SCSS identifiers:
+      // - CSS Syntax L3 §4.2 defines "ident code point" as including any
+      //   codepoint >= U+0080 (https://www.w3.org/TR/css-syntax-3/#ident-code-point)
+      // - CSS2 grammar includes `nonascii` in `nmstart`/`nmchar` productions
+      //   (https://www.w3.org/TR/CSS2/grammar.html#scanner)
+      // - Sass inherits CSS's <ident-token> grammar for identifiers
+      //   (https://github.com/sass/sass/blob/main/spec/syntax.md)
+      // Dart Sass handles them correctly, so we encode here as ASCII
+      // placeholders for analysis only, then decode in add-css-vars.ts.
+      contents = contents.replaceAll(
+        /[^\x00-\x7F]/g,
+        (ch) => `_u${ch.codePointAt(0)!.toString(16)}_`,
+      );
+
       // This is relatively painful, because unfortunately the error message of scss-parser
       // is not helpful.
 
diff --git a/tests/docs/smoke-all/2025/03/31/issue-12338/.gitignore b/tests/docs/smoke-all/2025/03/31/issue-12338/.gitignore
index 075b2542afb..0e3521a7d0f 100644
--- a/tests/docs/smoke-all/2025/03/31/issue-12338/.gitignore
+++ b/tests/docs/smoke-all/2025/03/31/issue-12338/.gitignore
@@ -1 +1,3 @@
 /.quarto/
+
+**/*.quarto_ipynb
diff --git a/tests/docs/smoke-all/2026/02/20/custom-14065-var.scss b/tests/docs/smoke-all/2026/02/20/custom-14065-var.scss
new file mode 100644
index 00000000000..eb66ab46056
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/20/custom-14065-var.scss
@@ -0,0 +1,7 @@
+/*-- scss:defaults --*/
+$présentation-bg: #ff0000;
+
+/*-- scss:rules --*/
+#test-unicode-var {
+  background-color: $présentation-bg;
+}
diff --git a/tests/docs/smoke-all/2026/02/20/custom-14065.scss b/tests/docs/smoke-all/2026/02/20/custom-14065.scss
new file mode 100644
index 00000000000..b420af861ee
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/20/custom-14065.scss
@@ -0,0 +1,5 @@
+/*-- scss:rules --*/
+
+#présentation p {
+  line-height: 2;
+}
diff --git a/tests/docs/smoke-all/2026/02/20/issue-14065-var.qmd b/tests/docs/smoke-all/2026/02/20/issue-14065-var.qmd
new file mode 100644
index 00000000000..585b37660b8
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/20/issue-14065-var.qmd
@@ -0,0 +1,15 @@
+---
+title: "Unicode SCSS Variable Test"
+format:
+  html:
+    theme:
+      - default
+      - custom-14065-var.scss
+_quarto:
+  tests:
+    html:
+      ensureCssRegexMatches:
+        - ['#test-unicode-var', '--quarto-scss-export-présentation-bg']
+---
+
+Content with a unicode-named color variable in SCSS.
diff --git a/tests/docs/smoke-all/2026/02/20/issue-14065.qmd b/tests/docs/smoke-all/2026/02/20/issue-14065.qmd
new file mode 100644
index 00000000000..a41c1e74583
--- /dev/null
+++ b/tests/docs/smoke-all/2026/02/20/issue-14065.qmd
@@ -0,0 +1,17 @@
+---
+title: "Unicode SCSS Test"
+format:
+  html:
+    theme:
+      - default
+      - custom-14065.scss
+_quarto:
+  tests:
+    html:
+      ensureCssRegexMatches:
+        - ['#présentation p', '--quarto-scss-export-']
+---
+
+## Présentation
+
+Unicode characters in headings become CSS selectors.