theming - fix editor background during DND

src/vs/workbench/browser/parts/editor/editorGroupsControl.ts

@@ -35,7 +35,7 @@ import { IWindowService } from 'vs/platform/windows/common/windows';
 import { getCodeEditor } from 'vs/editor/common/services/codeEditorService';
 import { IThemeService } from 'vs/platform/theme/common/themeService';
 import { editorBackground, highContrastBorder, highContrastOutline } from 'vs/platform/theme/common/colorRegistry';
-import { Themable, TABS_CONTAINER_BACKGROUND, EDITOR_HEADER_BACKGROUND, EDITOR_GROUP_BORDER_COLOR, EDITOR_DRAG_AND_DROP_BACKGROUND } from 'vs/workbench/common/theme';
+import { Themable, TABS_CONTAINER_BACKGROUND, EDITOR_HEADER_BACKGROUND, EDITOR_GROUP_BORDER_COLOR, EDITOR_DRAG_AND_DROP_BACKGROUND, EDITOR_GROUP_BACKGROUND } from 'vs/workbench/common/theme';
 
 export enum Rochade {
 	NONE,
@@ -1564,7 +1564,8 @@ export class EditorGroupsControl extends Themable implements IEditorGroupsContro
 	}
 
 	private updateFromDropping(element: HTMLElement, isDropping: boolean): void {
-		const background = this.getColor(isDropping ? EDITOR_DRAG_AND_DROP_BACKGROUND : null);
+		const groupCount = this.stacks.groups.length;
+		const background = this.getColor(isDropping ? EDITOR_DRAG_AND_DROP_BACKGROUND : groupCount > 0 ? EDITOR_GROUP_BACKGROUND : null);
 		element.style.backgroundColor = background;
 
 		const useOutline = this.isHighContrastTheme && isDropping;