app.js is COMPILED OUTPUT. Do not edit it by hand — your changes will be
overwritten the next time anyone rebuilds.

The source is resources/js/app.js.

To change the design you need Node on some machine (not the server):
    npm install
    npm run build
...then upload the regenerated public/css/app.js.

If you are not changing the design, you never need Node at all. The file
shipped here is already built.
