Large Images Not Displayed in Reveal.js Presentations on Mobile View

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

When rendering a Quarto document as a Reveal.js presentation, large images do not appear in mobile view, although they display correctly in desktop view.

Desktop View:

Mobile view:

Steps to reproduce

1. Create a Quarto Reveal.js presentation with large images
2. View the presentation on a mobile device or in mobile viewport mode
3. Navigate to slides containing stretched images

I've created a minimal reproducible example demonstrating this issue:

• Source code: https://github.com/danielvartan/test/tree/quarto-2
• Live demo (GitHub Pages): https://danielvartan.github.io/test

Actual behavior

Large/stretched images fail to render in mobile view.

Expected behavior

All slide content, including stretched images, should display correctly across all device types and screen sizes.

Your environment

Desktop:

• Quarto v1.8.27
• Positron Version: 2026.01.0 build 147
• Code - OSS Version: 1.106.0
• Commit: 3290136f699527bf01b703b390457b05ef2b858a
• Date: 2026-01-06T01:43:52.838Z
• Electron: 37.7.0
• Chromium: 138.0.7204.251
• Node.js: 22.20.0
• V8: 13.8.258.32-electron.0
• OS: Linux x64 6.18.2-arch2-1

Mobile:

• OS: Android 10
• Browsers tested: Firefox v148.0b4 (build #2016138863), Chrome v144.0.7559.76
• Result: Issue reproduces in both browsers

Quarto check output

 > quarto check
Quarto 1.8.27
[✓] Checking environment information...
      Quarto cache location: /home/danielvartan/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.3.1: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.8.27
      Path: /opt/quarto/bin

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

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: undefined

[✓] Checking Chrome Headless....................OK
      Chrome:  (not detected)

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

[✓] Checking Python 3 installation....OK
      Version: 3.13.11
      Path: /usr/bin/python3
      Jupyter: 5.9.1
      Kernels: python3

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

[✓] Checking R installation...........OK
      Version: 4.5.2
      Path: /usr/lib64/R
      LibPaths:
        - /home/danielvartan/R/x86_64-pc-linux-gnu-library/4.5
        - /usr/lib/R/library
      knitr: 1.51
      rmarkdown: 2.30

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

Start with the minimal reproducible example at https://github.com/danielvartan/test/tree/quarto-2 and compare its generated Reveal.js presentation in desktop and mobile viewport modes. Inspect how the stretched images are rendered on the affected slides, then verify against the live demo at https://danielvartan.github.io/test. Done means large images display on mobile devices and desktop without regressing other slide content.