CK-editor classic ckfinder error

Module parse failed: Unexpected character ‘@’ (6:0)
You may need an appropriate loader to handle this file type.
| */
| @import “./_hidden.css”;
| @import “./_reset.css”;
| @import “./_zindex.css”;

When i call beclow code

plugins: [CKFinder],

  // Enable the "Insert image" button in the toolbar.
  toolbar: ['imageUpload',],
  image: {
    toolbar: ['imageTextAlternative', '|', 'imageStyle:full', 'imageStyle:side']

  ckfinder: {
    // Upload the images to the server using the CKFinder QuickUpload command.
    uploadUrl: ''

The error occur.