[WIP] feat(v2): no-JS collapsible DocSidebar

[duanwilliam]

Motivation

#3030

PoC no-JS collapsible sidebar using hidden checkboxes. code is pretty sloppy at the moment but it is working. would probably need to cleaned up significantly.

some functionality may still be missing but it should look mostly similar to the existing one.

live demo at https://duanwilliam.github.io/docusaurus-purecss-sidebar/

WIP

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

Disable JS in browser and check

[netlify]

[V2]

Built without sensitive environment variables with commit eba670a

https://deploy-preview-4586--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	67
🟢 Accessibility	96
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4586--docusaurus-2.netlify.app/

[slorber]

Thanks for your POC @duanwilliam

I'm not going to follow-up on this because I think we should have "lazy sidebars" instead, and reduce the HTML markup rendered on the server to avoid rendering collapsed content: #5136
This is important for perf on sites rendering very large sidebars.

I think it's not useful anymore to allow uncollapsing categories of the sidebar with CSS/HTML only.
Instead, we'll solve the no-JS category uncollapsing by making the category a link targeting a page (category index page, or first doc of that category...), and the target page will have the category uncollapsed by default.
Track #2643