Feature/refresh docs 2025/css improvements

[Abhi-MS]

What kind of change does this PR introduce?

Updated CSS for refreshing docs.talawa.io website for 2025

Issue Number:

Only fixes one part of #916

Did you add tests for your changes?

No. Manual visual testing was done for the CSS updates.

Snapshots/Videos:

talawa.compressed.mp4

If relevant, did you update the documentation?

Not applicable. No update in the documentation was needed.

Summary

This pull request enhances the look and feel of the current website. The updated CSS provides a modern look.
Collapsible left drawer is removed. Dark/light modes capabilities are restored.

Does this PR introduce a breaking change?

No

Other information

The changes have been tested for cross-browser compatibility.

Have you read the contributing guide?

Yes

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[Abhi-MS]

Two changes were made to the docusaurus.config.js file. These changes are essential to meet the following requirements of the issue:

1. To enable dark/light mode
2. Remove default collapsable sidebar behaviour