src/vs/editor/browser/services/abstractCodeEditorService.ts/AbstractCodeEditorService/_getOrCreateStyleSheet
class AbstractCodeEditorService:	private _getOrCreateStyleSheet(editor: ICodeEditor | undefined): GlobalStyleSheet | RefCountedStyleSheet {
		if (!editor) {
			return this._getOrCreateGlobalStyleSheet();
		}
		const domNode = editor.getContainerDomNode();
		if (!dom.isInShadowDOM(domNode)) {
			return this._getOrCreateGlobalStyleSheet();
		}
		const editorId = editor.getId();
		if (!this._editorStyleSheets.has(editorId)) {
			const refCountedStyleSheet = new RefCountedStyleSheet(this, editorId, dom.createStyleSheet(domNode));
			this._editorStyleSheets.set(editorId, refCountedStyleSheet);
		}
		return this._editorStyleSheets.get(editorId)!;
	}