fix: accidentally deleted own styling

Author: wuweiweiwu

website/sandbox/index.js

@@ -4,6 +4,7 @@ import App from './App';
 
 // eslint-disable-next-line import/no-unresolved
 import 'react-sortable-tree/style.css';
+import './styles.css';
 
 const rootElement = document.getElementById('root');
 ReactDOM.render(<App />, rootElement);