* Add "Read the Docs" link below bottom CTA on homepage
* Increase top padding on Read the Docs link
* Reduce docs horizontal padding on mobile
* Align docs content with header on mobile, increase top padding
* Make sticky header fully opaque with subtle bottom border
* Fix sticky header on mobile by containing horizontal overflow in content area
Wide content (hierarchy diagrams, code blocks) was causing horizontal
page scroll, which breaks position:sticky on mobile browsers. Added
overflow-x:hidden to the main content area (below the header in DOM)
and overflow-x:auto to docs pre blocks so they scroll internally.
* Remove bottom border from sticky header
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