Can't resolve '@riophae/vue-treeselect/dist/vue-treeselect.css'

This error typically occurs when the required CSS file for the `@riophae/vue-treeselect` package cannot be resolved. Here are a few steps you can try to resolve this issue:

1. Make sure you have installed the `@riophae/vue-treeselect` package correctly. You can do this by running `npm install @riophae/vue-treeselect` or `yarn add @riophae/vue-treeselect` depending on your package manager.

2. Check if the `vue-treeselect.css` file is present in the correct location within the package. You can navigate to the package directory, locate the `dist` folder, and check if the CSS file exists.

3. Verify that you have configured your module bundler (such as webpack or rollup) correctly to handle CSS imports. Make sure you have appropriate loaders or plugins installed and configured to process CSS files.

4. If you are using a Vue CLI project, ensure that the CSS file is imported in your main `App.vue` or any other component where you are using `@riophae/vue-treeselect`. You can do this by adding the following line at the top of the component file:

   import '@riophae/vue-treeselect/dist/vue-treeselect.css';

If you have followed these steps and are still encountering the error, please provide more details about your project setup, including your package.json and any relevant configuration files, so that I can assist you further.