fix(theme): preserve gradio's --font / --font-mono css vars

The _OnyxAmberBase override redirected self.font into font_str, which
broke _get_theme_css emission of --font / --font-mono. Expose iterable
access via .font_list / .font_mono_list instead, and add a regression
assertion on the generated CSS.

tests/test_theme.py

@@ -28,8 +28,19 @@ def test_css_string_contains_critical_selectors():
 
 def test_fonts_geist_and_geist_mono():
     th = theme.build_theme()
-    # gr.themes.GoogleFont stringifies to its name
-    fonts = [str(f) for f in th.font]
+
+    # (a) Iterable lists: .font_list / .font_mono_list expose the original entries.
+    fonts = [str(f) for f in th.font_list]
     assert any("Geist" in f for f in fonts)
-    monos = [str(f) for f in th.font_mono]
+    monos = [str(f) for f in th.font_mono_list]
     assert any("Geist Mono" in f for f in monos)
+
+    # (b) CSS variables: _get_theme_css() must emit --font and --font-mono that
+    #     reference Geist / Geist Mono so the browser actually loads the fonts.
+    #     This assertion is what catches the original bug where property setters
+    #     redirected self.font → font_str, causing --font-str to be emitted instead.
+    css = th._get_theme_css()
+    assert "--font:" in css, "--font CSS variable missing from generated theme CSS"
+    assert "--font-mono:" in css, "--font-mono CSS variable missing from generated theme CSS"
+    assert "Geist" in css, "Geist font name missing from generated theme CSS"
+    assert "Geist Mono" in css, "Geist Mono font name missing from generated theme CSS"

theme.py

@@ -20,31 +20,24 @@ AMBER: dict[str, str] = {
 
 
 class _OnyxAmberBase(gr.themes.Base):
-    """gr.themes.Base subclass that exposes font/font_mono as lists of font objects.
+    """gr.themes.Base subclass with helpers for iterating over font lists.
 
-    In Gradio 5.x, Base.__init__ collapses font lists to a CSS string and assigns
-    them to self.font / self.font_mono.  The internal lists are kept on self._font
-    and self._font_mono.  This subclass redirects the public attributes to the
-    internal lists so callers can iterate over GoogleFont / str entries directly.
-    The CSS strings are preserved on self.font_str / self.font_mono_str.
+    Gradio collapses font lists into a CSS string at __init__; we expose the
+    original lists via .font_list / .font_mono_list for code that needs to
+    iterate.  The public self.font / self.font_mono attributes are left alone so
+    that _get_theme_css() emits the correct --font / --font-mono CSS variables.
     """
 
-    @property  # type: ignore[override]
-    def font(self) -> list:  # type: ignore[override]
+    @property
+    def font_list(self) -> list:
+        """Return the original font list (GoogleFont + str entries)."""
         return self._font
 
-    @font.setter
-    def font(self, val: str) -> None:
-        self.font_str = val
-
-    @property  # type: ignore[override]
-    def font_mono(self) -> list:  # type: ignore[override]
+    @property
+    def font_mono_list(self) -> list:
+        """Return the original monospace font list (GoogleFont + str entries)."""
         return self._font_mono
 
-    @font_mono.setter
-    def font_mono(self, val: str) -> None:
-        self.font_mono_str = val
-
 
 def build_theme() -> gr.themes.Base:
     """Return a Gradio theme matching the Onyx Amber palette."""