AsciiDoc underline is not working

[programmingkidx]

AsciiDoc underline does not work. I tried this code that was taken directly from the Asciidoc website:

Where did all the [.underline]#cores# go?

The result was a sentence without any formatting. The word "cores" should have been underlined.

I copied example 7 from here: https://docs.asciidoctor.org/asciidoc/latest/syntax-quick-reference/, and none of the formatting worked. This is the example:

Mark my words, #automation is essential#.

##Mark##up refers to text that contains formatting ##mark##s.

Where did all the [.underline]#cores# go?

We need [.line-through]#ten# twenty VMs.

A [.myrole]#custom role# must be fulfilled by the theme.