How to give a custom style to subtitle:?

[nipnipj]

We can customize title: header with:

h1.title {
  font-family: "Font name here";
}

How can we customize other header parts like subtitle: or author? Is there a public list of them?

[dragonstyle]

There is not a specific list. You have a couple of options - you can target them using css selectors (e.g. p.subtitle {...}) or you could provide your own title block template, which can emit any HTML that you'd like. More on customizing or replacing the title blocks here:

https://quarto.org/docs/authoring/title-blocks.html