src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts/NotebookEditorWidget/_createWebview
class NotebookEditorWidget:	private async _createWebview(id: string, resource: URI): Promise<void> {
		this._webview = this.instantiationService.createInstance(BackLayerWebView, this, id, resource, this._notebookOptions.computeWebviewOptions(), this.notebookRendererMessaging.getScoped(this._uuid));
		this._webview.element.style.width = '100%';

		// attach the webview container to the DOM tree first
		this._list.rowsContainer.insertAdjacentElement('afterbegin', this._webview.element);
	}