feat: add top and bottom sticky mobile navigation

[theetrain]

Changes

Svelte.Sticky.Mobile.Nav.Headers.mov

This was motivated by it being challenging for me to discover and navigate to CLI or MCP docs that are far down the navigation container.

Tested on:

• Chrome
• Firefox
• Safari

Test scenarios:

• Short viewport height, iPhone 13 and Pixel 7 portrait and landscape dimensions, 200% browser font size

Some notes:

• <section> elements were removed since they didn't seem to add more value than the nav headings themselves. Without aria-labelledby, the <section> elements didn't seem to serve much purpose; and with them gone, it's now possible to make section headings sticky on the top and bottom. I'll verify this later to make doubly sure since I'm running with the assumption that screen readers may navigate by headings sufficiently within the <nav> landmark.

Some todos:

• Add a vertical viewport media query to stack headings only when there's enough space; otherwise use a disclosure widget and collapse grouped headings as they sit on the top or bottom depending on the nav menu's scroll position.
• Consider denser grouping while headings are stacked.
• Consider special styling for headings while they are sticky, though we may be blocked from a CSS-only solution due to container queries yet being able to target elements that are stuck: https://caniuse.com/mdn-css_at-rules_container_scroll-state_queries.
• Test with various zoom levels and browser font sizes.

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• It's really useful if your PR references an issue where it is discussed ahead of time.
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.

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Project	Deployment	Actions	Updated (UTC)
svelte-dev	Ready	Preview	Feb 12, 2026 4:08am

[theetrain]

This was necessary to prevent headings from covering the 'back to docs' button.

[theetrain]

Taking this back to improve appearance on most phones since I didn't account for the iOS Safari URL bar:

• Change container query to height < 450px
• Make space between stacked headings denser
• Try adding a shadow to indicate there is more content to scroll into

[Rich-Harris]

super cool!