RFR: 8342705: Add dark mode for docs

[Nizar Benalla]

On Tue, 8 Jul 2025 13:22:20 GMT, Hannes Wallnöfer <hannesw at openjdk.org> wrote:

> 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](https://cr.openjdk.org/~hannesw/8342705/api.02/) (`java.base` module only). The docs were generated with syntax highlighting enabled in order to view the highlighting themes, although that is obviously not part of the change.

src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/resources/highlight.css line 71:

> 69:     .hljs-title.function_,
> 70:     .hljs-template-variable {
> 71:         color: #66bcce;

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

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PR Review Comment: https://git.openjdk.org/jdk/pull/26185#discussion_r2207819271