Responsive requirements

Files are read on phones, mostly. The 3:4 portrait cover scales beautifully on mobile (matches phone aspect ratio). The reader page has the most-tuned mobile behavior on the platform: sticky reader header collapses, TOC sidebar slides into a drawer, body sections maintain editorial typography rhythm.

Per-breakpoint behaviors

Mobile (≤640px)

Listing: 1-up grid. Cards taller because 3:4 covers stack. Details: hero stacks (cover on top, body below). Reader: sticky header collapsed; TOC accessible via a hamburger that opens a drawer. Body content occupies full width.

Tablet (641-1023px)

Listing 2-up. Details 2-column hero. Reader keeps the sticky header full-width; TOC drawer still used (sidebar starts at ≥1024px).

Desktop (≥1024px)

Listing 3-up. Details full layout. Reader: sticky TOC sidebar on the left, body in the center reading column, optional sticky reader header at top.

File-specific responsive rules

• 3:4 portrait cover maintains aspect ratio at every viewport. Editorial SVG fallback scales gracefully with `viewBox` settings.
• Reading progress bar always visible at the top of the reader, even on mobile.
• TOC active-section highlight works on mobile via IntersectionObserver — same logic as desktop.
• Download modal scales to full-screen on phones < 480px for touch-friendly form completion.