Storefront Mega Menus allows you to create enhanced full-width dropdowns that seamlessly integrate with your Storefront-powered WooCommerce shop.
Installation

Download the .zip file from your WooCommerce account.
Go to: WordPress Admin > Plugins > Add New to upload the file you downloaded.
Activate the extension.
Click Save Changes.

Usage
Storefront Mega Menus adds all its settings to WordPress Customizer, making it straightforward to use. Upon opening the Customizer at Appearance > Customize, navigate to Menus.