### Bug description

From a new website project created using

```
$ quarto create-project . --type website
```

Add `page-footer` as [illustrated in the documentation](https://quarto.org/docs/websites/website-navigation.html#page-footer) such as

```
  page-footer:
    left: "Copyright 2021, Norah Jones" 
```

make the render process fail with

```
ERROR: TypeError: Cannot read properties of undefined (reading 'style')

TypeError: Cannot read properties of undefined (reading 'style')
    at quartoBootstrapDefaults (file:///opt/quarto/bin/quarto.js:123006:80)
    at layerQuartoScss (file:///opt/quarto/bin/quarto.js:122686:9)
    at resolveBootstrapScss (file:///opt/quarto/bin/quarto.js:122735:22)
    at boostrapExtras (file:///opt/quarto/bin/quarto.js:124241:25)
    at themeFormatExtras (file:///opt/quarto/bin/quarto.js:125763:16)
    at Object.formatExtras (file:///opt/quarto/bin/quarto.js:125237:102)
    at async runPandoc (file:///opt/quarto/bin/quarto.js:79912:60)
    at async renderPandoc (file:///opt/quarto/bin/quarto.js:80945:26)
    at async Object.onRender (file:///opt/quarto/bin/quarto.js:86565:36)
    at async renderFiles (file:///opt/quarto/bin/quarto.js:86528:25)
```

## Additional Information

Single line page footer works as expected, for example

```
page-footer: "Copyright 2021, Norah Jones" 
```

## Environment

Output of `quarto check`

```
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.1: OK
      Dart Sass version 1.55.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.3.294
      Path: /opt/quarto/bin

[✓] 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...........(None)

      Unable to locate an installed version of R.
      Install R from https://cloud.r-project.org/
 ```

### Checklist

- [X] Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
- [X] Please [format your issue](https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us) so it is easier for us to read the bug report.
- [X] Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
- [X] Please document the operating system you're running. If on Linux, please provide the specific distribution.
- [X] Please provide the output of `quarto check` so we know which version of quarto and its dependencies you're running.
dragonstyle
2023-03-29T09:32:07Z
rgaiacs
bug triaged-to
v1.3
closed
Cannot read properties of undefined (reading 'style') due HTML page footer
https://github.com/quarto-dev/quarto-cli/issues/5016