Nested items in unordered list don't use correct symbols

[eric-schneider]

Maybe this was a conscious design choice (I don't remember), but usually the symbol for an unordered list item changes depending on the level of nesting. Currently all levels of nesting use the same disc symbol (see preview). Whereas the AsciiDoc/Antora default UIs (example) use disc, circle, and then square for all subsequent levels.