[Question] Do I need to include dropzone css to show the dragging hover

I have enable dropzone on assetManager and i think it works correctly. But I also notice that the hovering effect when the image is being dragNdrop is not working. I just see the text on the upper left corner. here is my initiation of the grapesjs.

import grapesjs from 'grapesjs';
import 'grapesjs-blocks-basic';

let editor = grapesjs.init({
    container: '#gjs',
    height: '100%',
    plugins: ['gjs-blocks-basic'],
    pluginOptions: {
        'gjs-blocks-basic': {}
    },

    // storemanager
    storageManager: {
        type: 1,
        autoload: 'none'
    },

    // asset manager
    assetManager: {
        upload: 'http://localhost/upload.php',
        dropzone: 1,
        dropzoneContent: '<div class="dropzone-inner">Drop here your assets</div>'
    }
});

as you can see there is no hovering effect just like what is shown here. https://github.com/artf/grapesjs/wiki/Assets#setup-dropzone