Spanners appear incorrect in tables produced with gt

[snhansen]

Bug description

Table spanners in gt-tables appear above the spanner label and not below as it should when rendering to html.

Steps to reproduce

---
format: html
---

```{r}
mtcars[1:3, 1:4] |> 
  gt::gt() |> 
  gt::tab_spanner(label = gt::md("Header"), columns = 2:3)
```

Expected behavior

Actual behavior

Your environment

• On Windows 11.
• gt v. 0.11.0

Quarto check output

Quarto 1.6.4
[>] Checking versions of quarto binary dependencies...
	  Pandoc version 3.2.0: OK
	  Dart Sass version 1.70.0: OK
	  Deno version 1.41.0: OK
	  Typst version 0.11.0: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
	  Version: 1.6.4
	  Path: C:\Users\au234616\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....OK
	  Version: 3.11.1
	  Path: C:/Users/au234616/AppData/Local/Programs/Python/Python311/python.exe
	  Jupyter: 5.2.0
	  Kernels: python3

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

[>] Checking R installation...........OK
	  Version: 4.4.0
	  Path: C:/PROGRA~1/R/R-44~1.0
	  LibPaths:
		- C:/Users/au234616/AppData/Local/R/win-library/4.4
		- C:/Program Files/R/R-4.4.0/library
	  knitr: 1.47
	  rmarkdown: 2.27

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

[cscheid]

Thanks, I can repro.

The typical html-table-processing: none workaround does apply here, so that might be something you want to use.

[cscheid]

This is currently a GT bug. The HTML doesn't validate. Quarto requires the HTML to validate before we can make promises about the behavior.

See below.

[cscheid]

(In the feature, please make sure to check if the HTML generated by GT validates before filing a bug. Thanks!)