Inactive selection bg in dom renderer

Part of #3803

src/browser/TestUtils.test.ts

@@ -5,7 +5,7 @@
 
 import { IDisposable, IMarker, ILinkProvider, IDecorationOptions, IDecoration } from 'xterm';
 import { IEvent, EventEmitter } from 'common/EventEmitter';
-import { ICharacterJoinerService, ICharSizeService, IMouseService, IRenderService, ISelectionService } from 'browser/services/Services';
+import { ICharacterJoinerService, ICharSizeService, ICoreBrowserService, IMouseService, IRenderService, ISelectionService } from 'browser/services/Services';
 import { IRenderDimensions, IRenderer, IRequestRedrawEvent } from 'browser/renderer/Types';
 import { IColorSet, ITerminal, ILinkifier2, IBrowser, IViewport, IColorManager, ICompositionHelper, CharacterJoinerHandler, IRenderDebouncer, IBufferRange } from 'browser/Types';
 import { IBuffer, IBufferStringIterator, IBufferSet } from 'common/buffer/Types';
@@ -340,6 +340,11 @@ export class MockCompositionHelper implements ICompositionHelper {
   }
 }
 
+export class MockCoreBrowserService implements ICoreBrowserService {
+  public serviceBrand: undefined;
+  public isFocused: boolean = true;
+}
+
 export class MockCharSizeService implements ICharSizeService {
   public serviceBrand: undefined;
   public get hasValidSize(): boolean { return this.width > 0 && this.height > 0; }