--- original
+++ modified
@@ -213,6 +213,10 @@
     /// Whether accessibility is active in this layout.
     /// (Note: this is a temporary field which will be replaced with an optional accessibility tree member.)
     accessibility_active: Cell<bool>,
+
+    /// The current page zoom for rendering (used by embedded webviews).
+    /// When this changes, we need to trigger a new stacking context tree build.
+    page_zoom_for_rendering: Cell<Option<f32>>,
 }

 pub struct LayoutFactoryImpl();
@@ -253,12 +257,25 @@
     fn set_viewport_details(&mut self, viewport_details: ViewportDetails) -> bool {
         let device = self.stylist.device_mut();
         let device_pixel_ratio = Scale::new(viewport_details.hidpi_scale_factor.get());
-        if device.viewport_size() == viewport_details.size &&
-            device.device_pixel_ratio() == device_pixel_ratio
-        {
-            return false;
+
+        // Check if page_zoom_for_rendering changed (for embedded webviews)
+        let zoom_changed =
+            self.page_zoom_for_rendering.get() != viewport_details.page_zoom_for_rendering;
+        if zoom_changed {
+            self.page_zoom_for_rendering
+                .set(viewport_details.page_zoom_for_rendering);
+            // Need to rebuild stacking context tree to apply the new zoom transform
+            self.need_new_stacking_context_tree.set(true);
+            self.need_new_display_list.set(true);
         }

+        let size_changed = device.viewport_size() != viewport_details.size ||
+            device.device_pixel_ratio() != device_pixel_ratio;
+
+        if !size_changed {
+            return zoom_changed;
+        }
+
         device.set_viewport_size(viewport_details.size);
         device.set_device_pixel_ratio(device_pixel_ratio);
         self.device_has_changed = true;
@@ -818,6 +835,7 @@
             paint_timing_handler: Default::default(),
             user_stylesheets: config.user_stylesheets,
             accessibility_active: Cell::new(config.accessibility_active),
+            page_zoom_for_rendering: Cell::new(config.viewport_details.page_zoom_for_rendering),
         }
     }