fix(revealjs): load default-theme Source Sans Pro via Google Fonts @import

The compiled Quarto reveal theme named `Source Sans Pro` in `--r-main-font` but
loaded no font face, so `q2 render` fell back to Helvetica on any machine
without Source Sans Pro installed — while `q2 preview` showed Source Sans Pro
(reveal's vendored white.css embeds it as a base64 @font-face). Surfaced in
end-to-end testing as "render points to the wrong fonts."

Fix per user decision: load Source Sans Pro from the Google Fonts CDN with a
foundry `@import` in the Quarto reveal layer's `scss:defaults`, mirroring the
named themes (Lato/Ubuntu/…) and Quarto 1's `_brand.yml` font model — rather
than bundling the font binaries. The render is intentionally not self-contained
for fonts, matching Quarto 1's import-based approach. A theme or `_brand.yml`
that sets a different `$font-family-sans-serif` supplies its own font and this
import is then unused (harmless), exactly as in Quarto 1's quarto.scss.

Sass hoists the CSS `@import url(...)` to the top of the compiled output (CSS
requires `@import` first); a test asserts both the import's presence and that it
precedes the first `.reveal` rule. E2E: `q2 render` + Chrome confirmed the
Source Sans Pro 400 face loads and applies.

Note: this fixes the render side only. The preview still shows reveal's stock
white.css look (centered text, uppercase headings, its own SSP) because the
q2-slides preview never applies the compiled Quarto reveal theme — full
per-document preview parity is the larger follow-up (bd-y259zb57, Level 2).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: cscheid

crates/quarto-sass/tests/integration/reveal_theme_test.rs

@@ -86,6 +86,26 @@ fn quarto_values_flow_into_custom_properties() {
     );
 }
 
+#[test]
+fn default_theme_imports_source_sans_pro_from_google() {
+    let css = compile(&assemble_reveal_scss(&[]).unwrap());
+    // The default theme loads its named font (Source Sans Pro) via a Google
+    // Fonts @import (Q1-style foundry import; no local bundling).
+    assert!(
+        css.contains("@import url(") && css.contains("Source+Sans+Pro"),
+        "default theme should @import Source Sans Pro from Google Fonts\n{css}"
+    );
+    // CSS requires @import to precede normal rules — confirm it is hoisted
+    // ahead of the first `.reveal` rule.
+    let imp = css.find("@import").expect("@import present");
+    if let Some(rule) = css.find(".reveal") {
+        assert!(
+            imp < rule,
+            "@import must come before CSS rules (CSS requires @import first)"
+        );
+    }
+}
+
 #[test]
 fn headings_are_not_uppercased() {
     let css = compile(&assemble_reveal_scss(&[]).unwrap());

resources/scss/revealjs/quarto-revealjs.scss

@@ -9,6 +9,17 @@
 
 /*-- scss:defaults --*/
 
+// Default body/heading font. Quarto 1's default reveal theme ships Source Sans
+// Pro; we load it from the Google Fonts CDN (a foundry @import, like the named
+// themes and `_brand.yml` fonts) rather than bundling the binaries — so the
+// render is not self-contained for fonts by design, matching Quarto 1's
+// import-based font model. A theme or `_brand.yml` that sets a different
+// `$font-family-sans-serif` supplies (and loads) its own font; this import is
+// then unused (harmless), exactly as in Quarto 1's `quarto.scss`. Sass hoists
+// the CSS `@import url(...)` to the top of the compiled output (CSS requires it
+// first), so its placement here in `scss:defaults` is fine.
+@import url(https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,400i,600,600i);
+
 // =============================================================================
 // Quarto's reveal.js layer (the Quarto-2 analogue of Quarto 1's quarto.scss).
 //