If you want to use text rather then icons font or standard PNG image files, then you have to activate line 22 and comment line 23.
@import "asciidoc/admonition-text.less"; //@import "asciidoc/admonition-iconsfont.less";
If you want to use only PNG image files ( with AsciiDoc icons
attribute ),
just remove or comment 23.
//@import "asciidoc/admonition-iconsfont.less";