app/vue.config.js

// vue.config.js
module.exports = {
    publicPath: process.env.BUILD_TARGET == 'app' ? '/' : '/rummy-timer/',
    outputDir: process.env.BUILD_TARGET == 'app' ? 'app': 'dist',
    css: {
        loaderOptions: {
            // by default the `sass` option will apply to both syntaxes
            // because `scss` syntax is also processed by sass-loader underlyingly
            // but when configuring the `prependData` option
            // `scss` syntax requires an semicolon at the end of a statement, while `sass` syntax requires none
            // in that case, we can target the `scss` syntax separately using the `scss` option
            scss: {
                additionalData: `@import "~@/scss/includes.scss";`
            },
        }
    }
}