Enhance layout of prefs-dialog.

data/panel-osd-settings.ui

@@ -15,6 +15,8 @@
   <object class="GtkBox" id="main-widget">
     <property name="height_request">1</property>
     <property name="can_focus">False</property>
+    <property name="valign">start</property>
+    <property name="vexpand">True</property>
     <property name="orientation">vertical</property>
     <child>
       <object class="GtkLabel" id="label-x-pos">
@@ -29,7 +31,7 @@
       </object>
       <packing>
         <property name="expand">False</property>
-        <property name="fill">True</property>
+        <property name="fill">False</property>
         <property name="position">0</property>
       </packing>
     </child>
@@ -210,5 +212,16 @@
         <property name="position">6</property>
       </packing>
     </child>
+    <child>
+      <object class="GtkSeparator" id="separator3">
+        <property name="visible">True</property>
+        <property name="can_focus">False</property>
+      </object>
+      <packing>
+        <property name="expand">False</property>
+        <property name="fill">True</property>
+        <property name="position">7</property>
+      </packing>
+    </child>
   </object>
 </interface>