Adjust stylesheets to render menubar items correctly.

There is a *bug in Qt5 (as of 5.3.1) where QMenuBar::items don't inherit their background colors, but revert to default system styling. The work around is to explicitly color their backgrounds.

files/styles/style-dark.css

@@ -334,6 +334,14 @@ QMenu::separator {
     margin: 8px 5px 4px 5px;
 }
 
+/*
+ * Fix for bug in Qt5 where QMenuBar items are styled natively on Windows, ignoring inherited settings.
+ * so we explicitly set their background color here (should match catch-all style background color).
+ */
+QMenuBar::item {
+    background-color: #222;
+}
+
 QMenuBar::item:selected {
     background-color: #CCC;
     color: #000;

files/styles/style-light.css

@@ -278,6 +278,14 @@ QMenu::separator {
     margin: 8px 5px 4px 5px;
 }
 
+/*
+ * Fix for bug in Qt5 where QMenuBar items are styled natively on Windows, ignoring inherited settings.
+ * so we explicitly set their background color here (should match catch-all style background color).
+ */
+QMenuBar::item {
+    background-color: #F6F6F6;
+}
+
 QMenuBar::item:selected {
     background-color: #555;
     color: #FFF;