What CSS processing steps are done?

[hyperknot]

First of all, thank you for this amazing software. I'm migrating from Substack to Astro + Listmonk for emails. I'm trying to figure out how to send good looking emails from either Markdown, or Markdown -> compiled HTML sources.

I noticed that in Listmonk when using Markdown or HTML modes, the CSS is processed/inlined.

Since CSS in emails is such a crazy complex topic, can you tell me what exactly is being done as automatic processing steps to Markdown and HTML emails?

Is Markdown processed just like HTML email, except for a first Markdown -> HTML step?