a11y: `opacity: 0.9` on h3 to h6 pushes links in headings below WCAG AA contrast

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2/5
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1-3 小时
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83/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
活跃
技术栈
css, html, sass

调研方向

从 src/resources/formats/html/bootstrap/_bootstrap-rules.scss 中报告所链接的标题不透明度规则处开始。渲染提供的 QMD 示例,并运行 axe-core 检查 h4、h5 和 h6 中链接的对比度。当这些链接保持主题链接颜色的对比度,且 axe-core 不再报告 color-contrast 违规时,即为完成。

由索引模型根据 Issue 内容生成。

描述

accessibility bug
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

The HTML stylesheet sets opacity: 0.9 on h3, h4, h5 and h6.
Opacity blends every descendant toward the page background, so a link colour that passes on its own fails inside a heading.
The built-in link colours are close to the 4.5:1 line, so there is no margin for the fade.

axe-core color-contrast (serious, WCAG 2.2 SC 1.4.3) flags a link inside h4, h5 and h6:

Theme Link colour after the fade Background Ratio
default #257dfd #ffffff 3.86:1
cosmo #3d71e6 #ffffff 4.46:1

A link inside h3 is not flagged, because h3 is large text and only needs 3:1.
Plain heading text is not flagged either.

#14679 reports the same mechanism for the appendix with opacity: 0.9.
This is a separate rule in a different place, so a fix for the appendix does not cover headings.

Steps to reproduce
---
title: "Heading link contrast test"
---

## Two

### Three [with a link](https://example.org)

#### Four [with a link](https://example.org)

##### Five [with a link](https://example.org)

###### Six [with a link](https://example.org)

Render it, then run axe-core on the page, for example with axe: output: document or with the axe.min.js that ships with Quarto.

Actual behavior

axe-core reports color-contrast on the links in the h4, h5 and h6 headings, with the ratios in the table above.

Expected behavior

Links inside headings keep the contrast of the theme's link colour, so they meet 4.5:1 whenever the link colour does.

Your environment
  • IDE: none, terminal only
  • OS: macOS (Darwin 27.0.0, Apple Silicon)
Quarto check output
Quarto 99.9.9
[✓] 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 Quarto installation......OK
      Version: 99.9.9
      commit: 69592e5c1718d3e1b2f3d11e757d32e23a16af67
主要语言
JavaScript
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