Where to write font-size if rem will be used?

Question

css

Let's say the document's font is 24px. For other elements, I want to set the font relative to these 24px.
According to the classics or whatever else they wrote best practice, as I understand it, the font size and so on are written in the body.

In my case, for rem to work, I have to write font-size: 24px in html.
Is it ok or not?

Answer 1

html, body {
 font-size: 24px;
}

Answer 2

html {
  font-size: [значение в px];
}