Backport dark mode support to API-M documentation versions below 4.6.0

Current Limitation

Summary

The API Manager documentation starting from version 4.6.0 includes a dark mode option, while all documentation versions below 4.6.0 (such as 4.5.0, 4.4.0, 4.3.0, and earlier) do not.

Many users still rely on these older documentation versions, and adding the same dark mode support would improve accessibility and provide a more consistent documentation experience across API-M releases.

Motivation

Dark mode improves readability, reduces eye strain, and offers a consistent user experience regardless of the documentation version being viewed.

Proposed Solution

Backport the dark mode implementation introduced in the 4.6.0 documentation to the documentation branches for versions below 4.6.0 where feasible.

I'm happy to work on implementing this enhancement and submit a pull request for review.

Suggested Improvement

Add the dark mode feature currently available in the 4.6.0 documentation to documentation versions below 4.6.0 (such as 4.5.0, 4.4.0, 4.3.0, and earlier where applicable).

Version

No response

Compare the dark mode implementation in the 4.6.0 API Manager documentation with the documentation branches for 4.5.0, 4.4.0, 4.3.0, and earlier where applicable. Identify the related CSS and documentation assets, then verify that the older versions provide the same dark mode experience without breaking their documentation builds.