Style code callouts differently from ordered lists

[bmorelli25]

Summary

From @colleenmcginnis in #175:

This is subjective, but I think we should consider styling the numbers below the code snippet differently than a regular ordered list in addition to adding number annotations to the code snippet itself.

From @marciw in the same issue:

+1 to this -- here's an example where even if the callout numbers were present in the code block, the regular ordered list below it might not look connected https://bookish-dollop-9p66716.pages.github.io/logs-data-stream.html#how-to-use-logsds
(compare https://www.elastic.co/guide/en/elasticsearch/reference/current/logs-data-stream.html#how-to-use-logsds)

[reakaleek]

Fixed by #346