src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts/NotebookEditorWidget/_registerDecorationType
class NotebookEditorWidget:	private _registerDecorationType(key: string) {
		const options = this.notebookEditorService.resolveEditorDecorationOptions(key);

		if (options) {
			const styleElement = DOM.createStyleSheet(this._body);
			const styleSheet = new NotebookRefCountedStyleSheet({
				removeEditorStyleSheets: (key) => {
					this._editorStyleSheets.delete(key);
				}
			}, key, styleElement);
			this._editorStyleSheets.set(key, styleSheet);
			this._decorationRules.set(key, new NotebookDecorationCSSRules(this.themeService, styleSheet, {
				key,
				options,
				styleSheet
			}));
		}
	}