How to end a header 3 box in rmarkdown beamer madrid presentation?

Question

When using the Madrid beamer theme (and some others) the Header 3 is rendered as a box covering the whole section, but in markdown the header is only specified at the start. How can I specify the end of the section?

In the example below, I want the second sentence to be inside the box, but the third to be back on the white background.

Example:

---
title: "Example"
output: 
  beamer_presentation:
    colortheme: beaver
    theme: Madrid
---

## Slide with Box

Hello, I'm not in the box

### This is a box
And this text is in the box!


I don't want to be in the box, but I am.

Output

Answer 1

This works for me:

## Slide with block 2

Hello, I'm not in the block.

\begin{block}{This is a block}
  And this text is in the block!
\end{block}


Hi, I'm not in the block either!

Answer 2

With newer versions of Pandoc (I have 2.2.3.2), you can use fenced divs to enclose a block. Did not work for me previously with 1.6.

Thus, this would work:

## Slide with Box

Hello, I'm not in the box

::: {.block}
### This is a box
And this text is in the box!
:::

I don't want to be in the box, and I am not.

::: {.block} and ::: delimit the block. See https://github.com/jgm/pandoc/issues/2957

An advantage with respect to using \begin{block} and \end{block} is that you get to use markdown within the block.