Dashboard: Sidebar changes layout

[AlbertRapp]

Bug description

Adding a sidebar changes the layout of the Quarto dashboard. Adding things like

format: 
  dashboard:
    orientation: rows

to the YAML header doesn't help with that.

Steps to reproduce

---
title: Reprex
format: dashboard
---

## {.sidebar}


## First Row

::: {.card}

First Col

:::

::: {.card}

Second Col

:::



## Second Row

::: {.card}

Full Row

:::

Expected behavior

Before adding ## {.sidebar} the layout was

AABB
CCCC

I expect the same to be true after adding the sidebar.

Actual behavior

After adding the sidebar the layout is

AAC
AAC
BBC
BBC

Your environment

• RStudio/2023.06.2+561
• Windows 10

Quarto check output

$ quarto check
Quarto 1.4.533
[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.11: OK
      Dart Sass version 1.69.5: OK
      Deno version 1.37.2: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
      Version: 1.4.533
      Path: C:\Users\Alber\AppData\Local\Programs\Quarto\bin
      CodePage: 1252

[>] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[>] Checking LaTeX....................OK
      Tex:  (not detected)

[>] Checking basic markdown render....OK

[>] Checking Python 3 installation....(None)

      Unable to locate an installed version of Python 3.
      Install Python 3 from https://www.python.org/downloads/

[>] Checking R installation...........OK
      Version: 4.2.1
      Path: C:/PROGRA~1/R/R-42~1.1
      LibPaths:
        - C:/Users/Alber/AppData/Local/R/win-library/4.2
        - C:/Program Files/R/R-4.2.1/library
      knitr: 1.44
      rmarkdown: 2.25

[>] Checking Knitr engine render......OK

[dragonstyle]

This is by design - the level 2 heading creating a sidebar is a 'column' on the page, and the other level 2 headings are also interpreted as columns (this isn't changeable at the page level since the sidebar is always a column since it is vertically oriented). You can keep the identical layout between the cases by changing the document to have a level 2 heading to contain the contents of the dashboard, and moving the current layout to level 3 headings, like so:

---
title: Reprex
format: dashboard
---

## {.sidebar}

## Main Body

### First Row

::: {.card}

First Col

:::

::: {.card}

Second Col

:::



### Second Row

::: {.card}

Full Row

:::

It's even easier to visualize using the alternative heading syntax for level 2 headings:

---
title: Reprex
format: dashboard
---

{.sidebar}
---------------


Body
---------------

### First Row

::: {.card}

First Col

:::

::: {.card}

Second Col

:::



### Second Row

::: {.card}

Full Row

:::