Update site section tabs with better column calc and animations

[zenoachtig]

Improves SiteSectionTabs dropdown behavior and simplifies the layout logic.

This fixes viewport positioning/close animation issues (fixed RND-10938), restores correct mobile width, tightens one-row and masonry sizing, and reduces some of the overgrown column-layout complexity while keeping the masonry behaviors intact.

CleanShot.2026-05-13.at.19.42.39.mp4

Also streamlines the layout a little bit to be more compact.

[linear-code]

RND-10938

[changeset-bot]

⚠️ No Changeset found

Latest commit: 0e3c15a

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-gamuhe7mt-gitbook.vercel.app	✅
Cloudflare	https://25e2593f-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-gamuhe7mt-gitbook.vercel.app/url/gitbook.com/docs	https://25e2593f-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-gamuhe7mt-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://25e2593f-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.gitbook.io/test-gitbook-open

[chatgpt-codex-connector]

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Build	Status	Details	Updated (UTC)
customers-v2-cloudflare (Inspect)	✅ No changes detected	-	Jun 10, 2026, 3:11 PM
customers-v2-vercel (Inspect)	✅ No changes detected	-	Jun 10, 2026, 3:10 PM
v2-cloudflare (Inspect)	👍 Changes approved	7 changed	Jun 10, 2026, 3:19 PM
v2-vercel (Inspect)	👍 Changes approved	6 changed	Jun 10, 2026, 3:16 PM