tweak the system menu theme

https://bugzilla.gnome.org/show_bug.cgi?id=706666

data/gnome-classic.css

@@ -222,6 +222,21 @@
     color: #666 !important;
   }
 
+/* SYSTEM MENU */
+
+.system-menu-action {
+    color: #e6e6e6;
+    border: 1px solid #ddd; /* using rgba() is flaky unfortunately */
+}
+
+.system-menu-action:hover,
+.system-menu-action:focus,
+.system-menu-action:active {
+    color: white;
+    background-color: #4a90d9;
+    border: none;
+}
+
 /* VOLUME SLIDER */
 
 .slider {
@@ -264,4 +279,4 @@
 .system-menu-action:hover,
 .system-menu-action:focus {
     color: black !important;
-}
+}