_StyleSheet : Darken MenuButtons added to main MenuBar

Our default style stands out as a bit bright against the dark MenuBar background.

While only necessary for the RenderPassChooserWidget, this has been applied generally so any future MenuButtons also get the same treatment.

python/GafferUI/_StyleSheet.py

@@ -1538,7 +1538,18 @@ def styleColor( key ) :
 		padding: 2px;
 	}
 
-	*[gafferClass="GafferUI.EditScopeUI.EditScopePlugValueWidget"] QPushButton[gafferWithFrame="true"][gafferMenuIndicator="true"]
+	#gafferMenuBarWidgetContainer QPushButton[gafferWithFrame="true"][gafferMenuIndicator="true"]
+	{
+		border: 1px solid rgb( 70, 70, 70 );
+		border-top-color: rgb( 108, 108, 108 );
+		border-left-color: rgb( 108, 108, 108 );
+		background-color : qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 rgb( 108, 108, 108 ), stop: 0.1 rgb( 91, 91, 91 ), stop: 0.90 rgb( 81, 81, 81 ));
+		margin-top: 2px;
+		margin-bottom: 2px;
+	}
+
+	*[gafferClass="GafferUI.EditScopeUI.EditScopePlugValueWidget"] QPushButton[gafferWithFrame="true"][gafferMenuIndicator="true"],
+	#gafferMenuBarWidgetContainer *[gafferClass="GafferUI.EditScopeUI.EditScopePlugValueWidget"] QPushButton[gafferWithFrame="true"][gafferMenuIndicator="true"]
 	{
 		border: 1px solid rgb( 46, 75, 107 );
 		border-top-color: rgb( 75, 113, 155 );