[docs] Add collapsible sidebar support

[pbanakar]

Purpose

This pull request adds support for a collapsible documentation sidebar on the Apache Fluss website. Users can collapse the left sidebar to expand the main reading area and easily expand it back. This idea was inspired from apache paimon.

Brief change log

• Configured themeConfig.docs.sidebar.hideable: true in website/docusaurus.config.ts to enable collapsible sidebar support with state persistence.
• Scoped blog button rules (.button.button--secondary and ::after arrow) in website/src/css/custom.css to prevent unintended styling and pseudo-elements on the sidebar collapse button.
• Added custom styles for the bottom sidebar collapse bar (<<) and left-edge expand button (>>) to ensure seamless theming and smooth hover transitions in both light and dark modes.
• Verified that desktop and mobile/tablet drawer navigation work cleanly without layout regressions.

Tests

• Manually tested desktop sidebar collapse and expand behavior in both light and dark modes.
• Manually verified responsive behavior on mobile/tablet viewports.

here are some looks

---

API and Format

Does not affect API or storage format.

Documentation

Does not introduce changes to documentation content.

[pbanakar]

Hi @wuchong @polyzos Can you please take a look on this ?

[polyzos]

@pbanakar assigned.. is this ready for review?

[pbanakar]

@pbanakar assigned.. is this ready for review?

Thanks! @polyzos yes ready for review, working fine in local.

[wuchong]

@pbanakar Thanks for working on this! This might be my personal thoughts. I’d prefer to keep the sidebar always visible for now. My main concern is that the collapse button at the bottom feels visually intrusive and doesn’t fit particularly well with the website’s clean design. Although it adds an optional interaction, it still adds visual clutter, and we haven’t seen a clear user need for it yet.

While Paimon offers this feature, I also checked the documentation sites for Flink, Iceberg, Pulsar, LanceDB, Doris, React, Docker, Kubernetes, Claude Code, and Restate. I didn’t find an option to hide the entire left sidebar in their desktop layouts. Keeping navigation visible is a common, well-established approach in technical documentation, helping readers understand the documentation structure and move between related sections.

If the goal is to give the main content more room, we could consider making the sidebar slightly narrower while keeping its labels readable. That would improve space utilization while preserving visible navigation and a clean interface.

What do you think?

[pbanakar]

Thanks @wuchong for the feedback, That makes complete sense. Since the current layout and sidebar spacing already provide sufficient room for content, I agree we don't need the collapsible toggle or width adjustments at this time.

I'll close this PR. Thanks again for the review and Suggestion!