src/vs/workbench/contrib/notebook/browser/viewParts/notebookTopCellToolbar.ts/ListTopCellToolbar/updateClass
class ListTopCellToolbar:	private updateClass() {
		if (this.notebookEditor.hasModel() && this.notebookEditor.getLength() === 0) {
			this.topCellToolbar.classList.add('emptyNotebook');
		} else {
			this.topCellToolbar.classList.remove('emptyNotebook');
		}
	}