LibWeb/SVG: Resolve fill URI reference values

Author: https://github.com/tcl3
Commit: 05432d7157
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5932
Reviewed-by: https://github.com/gmta ✅

Libraries/LibWeb/SVG/SVGGraphicsElement.cpp

@@ -161,13 +161,19 @@ Optional<Gfx::Color> SVGGraphicsElement::fill_color() const
 {
     if (!layout_node())
         return {};
-    // FIXME: In the working-draft spec, `fill` is intended to be a shorthand, with `fill-color`
-    //        being what we actually want to use. But that's not final or widely supported yet.
-    return layout_node()->computed_values().fill().map([&](auto& paint) -> Gfx::Color {
-        if (!paint.is_color())
-            return Color::Black;
-        return paint.as_color();
-    });
+
+    auto paint = layout_node()->computed_values().fill();
+    if (!paint.has_value())
+        return {};
+
+    if (paint->is_url()) {
+        if (auto referenced_element = try_resolve_url_to<SVGGraphicsElement const>(paint->as_url()))
+            return referenced_element->fill_color();
+
+        return {};
+    }
+
+    return paint->as_color();
 }
 
 Optional<Gfx::Color> SVGGraphicsElement::stroke_color() const