8342705: Add dark mode for docs

[hns]

Please review an enhancement to add a dark theme to javadoc-generated API documentation. There is a new button in the top right corner that brings up a menu to switch between themes. Available options are "Light", "Dark", and "System Setting" (following the system-wide theme setting). The selected theme is stored and preserved across browser sessions.

Generated docs can be viewed here (iteration 5, module java.base only).

Screenshots below show both themes and how to switch between them.

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Progress

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Issue

• JDK-8342705: Add dark mode for docs (Enhancement - P4)

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Update a local copy of the PR:
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[mlbridge]

Webrevs

• 02: Full - Incremental (a12a273c)
• 01: Full (dfb3b247)
• 00: Full (a35877de)

[hns]

I'm finding the orange link color a bit too flashy, so I created a new snapshot that uses a pale blue color for links. This results in a less striking color scheme that is more in line with the default light theme IMO.

I also realized that there is no requirement in terms of a11y to use a particular link color for navigation links, so I switched to a neutral color for links in the subnavigation and sidebar, which further "calms" the layout and improves readability IMO.

I haven't updated the PR yet and posting this here for discussion.

[nizarbenalla]

I don't think you can nest rules here, the browser may skip/ignore them.

[hns]

It works for me, I've tried it on Firefox, Safari and Chrome.

Documentation of CSS nesting: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_nesting/Using_CSS_nesting
It's implemented in all major browsers: https://caniuse.com/?search=css%20nesting

[hns]

I updated the PR with changes described in my previous comment.

[hns]

Another iteration on this PR, moving the theme switcher icon in line with the main navigation links in the top navigation bar.

I updated screenshots and demo docs.