import lwcTypescriptPlugin from 'rollup-plugin-lwc-typescript';
import lwcRollUpPlugin from "@lwc/rollup-plugin";
...
 
function rollupConfig() {
    return {
        input: path.resolve(__dirname, "components.js"),
        output: {
            file: path.join(__dirname, "build", "app.js"),
            format: "esm"
        },
        plugins: [
            lwcTypescriptPlugin(),
            lwcRollupPlugin({
                modules: "src/modules",
                stylesheetConfig: {
                    customProperties: { allowDefinition: true }
                }
            })
        ]
}