migration docs: Updates

Mention shadow type, relief, aspect frame.

docs/reference/gtk/migrating-3to4.xml

@@ -563,6 +563,12 @@
         and always use the context's current state. Update all callers
         to omit the state argument.
       </para>
+      <para>
+        The most commonly used GtkStyleContext API, gtk_style_context_add_class(),
+        has been moved to GtkWidget as gtk_widget_add_css_class(), as have the
+        corresponding gtk_style_context_remove_class() and
+        gtk_style_context_has_class() APIs.
+      </para>
     </section>
 
     <section>
@@ -587,6 +593,17 @@
       </para>
     </section>
 
+    <section>
+      <title>Stop using GtkShadowType and GtkRelief properties</title>
+      <para>
+        The shadow-type properties in GtkScrolledWindow, GtkViewport,
+        and GtkFrame, as well as the relief properties in GtkButton
+        and its subclasses have been removed. GtkScrolledWindow, GtkButton
+        and GtkMenuButton have instead gained a boolean has-frame
+        property.
+      </para>
+    </section>
+
     <section>
       <title>Adapt to GtkWidget's size request changes</title>
       <para>
@@ -1037,6 +1054,15 @@
       </para>
     </section>
 
+    <section>
+      <title>GtkAspectFrame is no longer a frame</title>
+      <para>
+        GtkAspectFrame is no longer derived from GtkFrame and does not
+        place a label and frame around its child anymore. It still lets
+        you control the aspect ratio of its child.
+      </para>
+    </section>
+
     <section>
       <title>Stop using custom tooltip windows</title>
       <para>