Inactive selection bg in dom renderer

Part of #3803

src/common/services/Services.ts

@@ -250,8 +250,9 @@ export interface ITheme {
   background?: string;
   cursor?: string;
   cursorAccent?: string;
-  selectionBackground?: string;
   selectionForeground?: string;
+  selectionBackground?: string;
+  selectionInactiveBackground?: string;
   black?: string;
   red?: string;
   green?: string;