src/vs/base/browser/ui/list/listWidget.ts/List/_onSelectionChange
class List:	private _onSelectionChange(): void {
		const selection = this.selection.get();

		this.view.domNode.classList.toggle('selection-none', selection.length === 0);
		this.view.domNode.classList.toggle('selection-single', selection.length === 1);
		this.view.domNode.classList.toggle('selection-multiple', selection.length > 1);
	}