Tweak language dropdown styling

[zenoachtig]

This removes the persistent border between the language selector and section tabs, in favour of a border that only appears when there is actually scrollable content. The new leadingEdgeScrollClassName and trailingEdgeScrollClassName props on the ScrollContainer component conditionally get added when there is an overscroll on either edge.

[changeset-bot]

🦋 Changeset detected

Latest commit: 47935b1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
gitbook	Patch

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-178fle5cw-gitbook.vercel.app	✅
Cloudflare	https://2bda5eb1-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-178fle5cw-gitbook.vercel.app/url/gitbook.com/docs	https://2bda5eb1-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-178fle5cw-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://2bda5eb1-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.gitbook.io/test-gitbook-open

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Build	Status	Details	Updated (UTC)
customers-v2 (Inspect)	✅ No changes detected	-	Oct 22, 2025, 2:59 PM
v2-cloudflare (Inspect)	👍 Changes approved	3 changed	Oct 22, 2025, 3:02 PM
v2-vercel (Inspect)	👍 Changes approved	3 changed	Oct 22, 2025, 3:01 PM