Since Reynir mentioned they use the Commonmark-HTML renderer, I’ll just add that I’m doing the same thing in a side project of mine and am pretty happy with the result:
However, I do intend to write my own ‘safe’ renderer by traversing the parsed Markdown AST and keeping only the HTML markup I want to support. I was doing that with omd before I replaced it with cmarkit and started using the built-in renderer intending to make some progress and revisit it later.