Default Jupyter Book build web accessibility issues

[d33bs]

Describe the bug

Thanks for the great work on this project, it's awesome! In beginning to develop content through Jupyter Book I noticed there are several web accessibility issues which are present in the default builds. These seem like they could be addressed to help meet web accessibility standards. I tried searching for existing issues which cover this and noticed none that are still open. #436 acknowledges existing web accessibility issues but was closed due to not being specific / actionable enough. My hope here is to provide specific and actionable feedback on what could be addressed in the default builds using Jupyter Book.

Specifically, I see that the following are issues based on WCAG 2 AA conformance standards.

// search form has no submit button
"WCAG2AA.Principle3.Guideline3_2.3_2_2.H32.2",
// heading tags detected with no content
"WCAG2AA.Principle1.Guideline1_3.1_3_1.H42.2",
// search form duplicate id
"WCAG2AA.Principle4.Guideline4_1.4_1_1.F77"

Please see below for a reference to some example code which may be used to demonstrate these issues.

If possible, I'd also be interested in hearing about potential workarounds to help remedy the issues through template customization, etc. Just the same, it feels important that these are addressed in the default builds from Jupyter Book. Thank you for any thoughts or guidance you have on this topic!

Reproduce the bug

I used pa11y on the HTML files created from jupyter-book build using mostly default settings. Please see here for a reference to a GitHub Actions workflow run with the results that cite the above failure codes.

List your environment

Jupyter Book      : 1.0.0
External ToC      : 1.0.1
MyST-Parser       : 2.0.0
MyST-NB           : 1.0.0
Sphinx Book Theme : 1.1.2
Jupyter-Cache     : 1.0.0
NbClient          : 0.9.0

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