How to use theme from classpath?

[david0]

I would like to use a custom theme thats located in the root of the classpath. How to do that?
I always get: SCHWERWIEGEND: could not locate or load the built-in pdf theme our-theme.yml'; reverting to default theme`

This is what I tried:

Attributes attributes = new Attributes();
attributes.setAttribute("pdf-style", "our-theme.yaml")

Options options = new Options();
options.setBackend("pdf");
options.setAttributes(attributes);

asciidoctor.convertFile(file, options)