asciidoctor-pdf and monospaced font in table

I'am writing my first ADOC document. It contains a table. I have such columns definition:
   [cols="6a,<35a,45m,12a"]
The conversion of the document to PDF turned out well. Just monospaced font turned red - but I would like it to be black.
Probably I have to modify/create some theme file, isn't it? Where and how best to do it?