Not possible to change theme in classic ui

Based on Using Existing Themes :: Jmix Documentation

I would like to change the theme and change in application.properties
jmix.ui.theme.name=halo

When I start now the application I get

2023-07-06 12:13:03.431 INFO 15324 — [nio-8080-exec-8] com.vaadin.server.VaadinServlet : Requested resource [/VAADIN/themes/halo/styles.css] not found from filesystem or through class loader. Add widgetset and/or theme JAR to your classpath or add files to WebContent/VAADIN folder.

In the market place I don’t find this theme anymore.

When i create a custom theme based on Creating a Custom Theme :: Jmix Documentation and start with the imports, i just get errors.

@import "addons";
@import "../halo/halo";

Is the documentation outdated or what do I miss ?

In the build directory I find the correct structure, but not in the studio ?

jmix.ui.theme.name = helium-extended
jmix.ui.theme-config = ui/ex1/theme/helium-extended-theme.properties