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!