Filament styling missing after upgrade

I'm trying to upgrade to v3. I followed the steps.

I created a new v3 project for comparison.
I'm seeing http://localhost/css/filament/filament/app.css?v=3.0.16.0 being fetched by the browser in the new project, but not in the upgraded one. I can't find the place where this is included / where I should add something.

Any idea?

Solution

Yes. That should be in the Theme instructions, too.