src/vs/workbench/browser/parts/editor/tabsTitleControl.ts/TabsTitleControl/updateDropFeedback
class TabsTitleControl:	private updateDropFeedback(element: HTMLElement, isDND: boolean, index?: number): void {
		const isTab = (typeof index === 'number');
		const editor = typeof index === 'number' ? this.group.getEditorByIndex(index) : undefined;
		const isActiveTab = isTab && !!editor && this.group.isActive(editor);

		// Background
		const noDNDBackgroundColor = isTab ? this.getColor(isActiveTab ? TAB_ACTIVE_BACKGROUND : TAB_INACTIVE_BACKGROUND) : '';
		element.style.backgroundColor = (isDND ? this.getColor(EDITOR_DRAG_AND_DROP_BACKGROUND) : noDNDBackgroundColor) || '';

		// Outline
		const activeContrastBorderColor = this.getColor(activeContrastBorder);
		if (activeContrastBorderColor && isDND) {
			element.style.outlineWidth = '2px';
			element.style.outlineStyle = 'dashed';
			element.style.outlineColor = activeContrastBorderColor;
			element.style.outlineOffset = isTab ? '-5px' : '-3px';
		} else {
			element.style.outlineWidth = '';
			element.style.outlineStyle = '';
			element.style.outlineColor = activeContrastBorderColor || '';
			element.style.outlineOffset = '';
		}
	}