[rich-iannone]

When navigating between pages, I noticed a few FOUT-like things (the navbar would disappear and reappear, the sidebar would briefly show unstyled links without headers or icons, and the "On This Page" header would pop in last). This happened because theme-init.js runs from include-in-header, which Quarto places after <body>, not inside the <head>.

This PR fixes this with an inline <style> in the metadata.html Pandoc partial now hides the page before any body content renders. The previous approach used visibility: hidden, but child elements with visibility: visible !important (sidebar sections, TOC) could leak through, so the fix also adds opacity: 0 on <body> which children cannot override. A double requestAnimationFrame in the reveal ensures after-body scripts (sidebar, dark-mode toggle, tags, etc.) have painted before the page becomes visible. A <noscript> fallback keeps pages visible when JavaScript is disabled.

Note that this fix doesn't address keeping the navbar on the screen while loading a new page. That's something that could be done in a separate PR (more involved of a fix).

[github-actions]

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