I spent a few hours chasing down just how to get my static assets (css, fonts, images) to load in an Electron app built using electron-forge v6 (https://www.electronforge.io/) and its webpack plugin (https://www.electronforge.io/config/plugins/webpack) while in development mode. There really isn't any documentation available online, either in the electron-forge documentation or in places like blogs or gists or stackoverflow. So I thought I'd put it down here.
npm i -D copy-webpack-plugin
Use the plugin to move your directories into place.