I prefer to style 2.

Style 2 , because it have the best balance.

3 levels in the left sidebar gives enough context to understand where you are.
Compared with Style 1, it reduces the risk of losing important hierarchy.
Compared with Style 3, it avoids forcing users to navigate 4+ levels before reaching content.

I prefer option Style 3, simple like a tree folder, classic but organized

I like style 1

I vote for style 3. It's UI/UX is clean and more presentable without complex navigation

Style 2.

Style 3

I vote for Style 2.

Reasoning:
When managing complex network deployments and referencing deep configuration guides, finding the exact information quickly without losing context is critical. Style 2 strikes the perfect balance. Having 3 levels on the left sidebar provides just enough structural context so I know exactly where I am within a broad topic (like a specific firewall module or server setting).

At the same time, retaining the right-hand Page Directory is essential. It allows for quick jumping to specific parameters or configuration steps on long pages. Style 1 hides too much of the hierarchy, while Style 3 clutters the left menu and removes the quick in-page navigation.

Suggestion:
Please ensure that the right-hand Page Directory is "sticky" (stays visible as we scroll down the page). This way, we never have to scroll back to the top just to jump to another sub-heading.

I like style 1.

My vote is for Style 1. It is simple, and user friendly.

Style 1's 2 levels feels too shallow for technical docs  users lose context on where they are in the hierarchy. Style 3's 4+ levels with no Page Directory makes in-page navigation harder for long articles, especially troubleshooting guides with multiple steps.I like style 2

Style 2 hits the right balance: enough sidebar depth for orientation, plus the Page Directory for quick in-page jumps. This mirrors what modern docs platforms (Stripe, Microsoft Learn) do — balancing hierarchy context with in-page navigation.