src/vs/workbench/contrib/notebook/browser/contrib/outline/notebookOutline.ts/NotebookOutlineRenderer/renderTemplate
class NotebookOutlineRenderer:	renderTemplate(container: HTMLElement): NotebookOutlineTemplate {
		container.classList.add('notebook-outline-element', 'show-file-icons');
		const iconClass = document.createElement('div');
		container.append(iconClass);
		const iconLabel = new IconLabel(container, { supportHighlights: true });
		const decoration = document.createElement('div');
		decoration.className = 'element-decoration';
		container.append(decoration);
		return new NotebookOutlineTemplate(container, iconClass, iconLabel, decoration);
	}