Update site layout and blocks with container queries

[zenoachtig]

• Introduce @container to Header, Footer, and PageBody. This lets elements size themselves to the available container width instead of the screen width. Widgets like the GitBook Assistant window will reduce the available width on the same screen size. This fixes a host of layout issues in the main content by the introduction of the Assistant window.

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• Also add @container to the Columns block, allowing blocks within columns to resize themselves to the available space.

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• Add responsive typography based on container size, making for better typography on very small screens.

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• Add @starting-style transitions to PageAside, allowing it to fade in an out when displayed, for example when the Assistant window replaces it.

• Add hydrated class to page root when the page is loaded. This helps scope animations on page load or after site load.

[changeset-bot]

🦋 Changeset detected

Latest commit: 94ae4fc

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

This PR includes changesets to release 1 package

Name	Type
gitbook	Minor

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[github-actions]

Summary of the deployments:

Version	URL	Status
Vercel	https://gitbook-v2-77loofx2f-gitbook.vercel.app	✅
Cloudflare	https://c10b01c4-gitbook-open-v2-preview.gitbook.workers.dev	✅

Test content

Site	2v	2c
GitBook	https://gitbook-v2-77loofx2f-gitbook.vercel.app/url/gitbook.com/docs	https://c10b01c4-gitbook-open-v2-preview.gitbook.workers.dev/url/gitbook.com/docs
E2E	https://gitbook-v2-77loofx2f-gitbook.vercel.app/url/gitbook.gitbook.io/test-gitbook-open	https://c10b01c4-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)	⚠️ Changes detected (Review)	156 changed	Nov 5, 2025, 4:34 PM
v2-cloudflare (Inspect)	⚠️ Changes detected (Review)	687 changed, 2 failures	Nov 5, 2025, 4:38 PM
v2-vercel (Inspect)	⚠️ Changes detected (Review)	695 changed, 2 failures	Nov 5, 2025, 4:38 PM