The axe check misses revealjs contrast at desktop viewports

[cwickham]

I have

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

In a revealjs deck, the axe option reports no color-contrast results at desktop viewports. It does report them at a narrow viewport, such as 320x568. The same gap occurs in quarto call axe.

At desktop sizes, reveal.js puts the slide backgrounds in a separate .reveal .backgrounds layer. This layer is behind the slide text, but it is not an ancestor of the text. As a result, axe cannot find the background color. It marks each text node as "incomplete" with the bgOverlap message: "Element's background color could not be determined because it is overlapped by another element".

The document and console reporters show only result.violations (document, console). The json reporter prints the full result, so the incomplete nodes are there, but they are not marked as a problem (json). quarto call axe requests only violations (scan.ts). Thus, contrast failures in revealjs are not visible.

At 320x568, reveal.js changes to scroll view. In scroll view, the backgrounds are inside the slide, and axe can find the color.

Before the scan, revealUnhideSlides() removes hidden and aria-hidden from the slides. It does not change the backgrounds layer.

Steps to reproduce

---
format:
  revealjs:
    axe:
      output: document
footer: "[quarto.org](https://quarto.org)"
---

## Slide

See [the Quarto website](https://quarto.org).

[This grey text fails contrast.]{style="color: #ccc"}

Preview and navigate to Accessibility Report slide.

Actual behavior

At 1440x900, the report shows no color-contrast findings. axe marks five nodes as incomplete: the heading, the body text, the grey text, the body link, and the footer link.

Viewport	color-contrast violations	Incomplete nodes
1440x900	none	5
1050x700	none	5
1000x660	none	5
320x568	grey text (1.6:1), footer link (4.43:1)	0

Expected behavior

The report shows the two contrast failures at all viewports: the grey text at 1.6:1 and the footer link at 4.43:1.

Your environment

• IDE: none (Chrome 150 through Playwright)
• OS: macOS 26.6.2 (build 25G83)

Quarto check output

Quarto 1.11.4
[✓] Checking environment information...
      Quarto cache location: /Users/charlottewickham/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.10.0: OK
      Dart Sass version 1.101.0: OK
      Deno version 2.7.14: OK
      Typst version 0.15.1: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.11.4
      Path: /Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2026.04
      Chrome Headless Shell: 150.0.7871.115
      VeraPDF: 1.28.2

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /Users/charlottewickham/Library/TinyTeX/bin/universal-darwin
      Version: 2026

[✓] Checking Chrome Headless....................OK
      Using: Chrome Headless Shell installed by Quarto
      Path: /Users/charlottewickham/Library/Application Support/quarto/chrome-headless-shell/chrome-headless-shell-mac-arm64/chrome-headless-shell
      Version: 150.0.7871.115

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

[✓] Checking R installation...........OK
      Version: 4.6.0
      Path: /Library/Frameworks/R.framework/Versions/4.6/Resources
      LibPaths:
        - /Users/charlottewickham/Library/R/arm64/4.6/library
        - /Library/Frameworks/R.framework/Versions/4.6/Resources/library
      knitr: 1.51
      rmarkdown: 2.31

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

[✓] Checking Python 3 installation....OK
      Version: 3.12.2
      Path: /Users/charlottewickham/.pyenv/versions/3.12.2/bin/python3
      Jupyter: 5.9.1
      Kernels: python3

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

[✓] Checking Julia installation...

I used an AI tool for this investigation. The results come from a local clone of quarto-cli and a local reproduction.