Annual Letter · 年度信笺

Produce a single-file, letter-grade HTML deck in the Stripe Annual Letter genre: a published letter you read, not a template you skim. Prose flows in serif paragraphs; numbers live in inline data cards and giant display anchors. The visual system, canvas contract, and navigation runtime are locked by example.html. Start from example.html, replace content only — do not rewrite the design or the script, and never introduce colors or fonts outside this spec.

Adapted from the editorial-longform style (references/design-styles.md, 安静派 · 杂志编辑长文流 / Editorial Longform) of huashu-design by 花叔 (alchaincyf), MIT licensed. Reference lineage: Stripe Annual Letter, Amazon six-page narrative memos, Stripe Press.

Hard spec (locked — violating any line is a regression)

Canvas & scaling

• One <div id="stage"> fixed at 1920 × 1080 px, centered with position: fixed; top: 50%; left: 50%.
• A fit() function scales the stage to the viewport: scale = min(innerWidth / 1920, innerHeight / 1080), applied as translate(-50%, -50%) scale(s), re-run on resize. Letterboxed, never cropped.
• All layout inside the stage uses px (never vw/vh/% for type) — the scaler owns responsiveness.

Slides & navigation runtime (do not rewrite the script)

• Each page is one <section class="slide"> directly inside #stage, with a data-screen-label="01 刊头"-style label (1-indexed).
• Exactly one slide carries .active. No .dark pages in this theme — every page sits on cream paper; rhythm comes from density, not theme flips.
• Keyboard: ←/↑/PageUp previous · →/↓/Space/PageDown next · Home/End first/last. Hash routing #/N (1-indexed) read on load and hashchange, written via history.replaceState. Click: left third back, rest forward. Fixed counter pill bottom-right, key-hint bottom-left.
• Zero external JS, zero build step; the file must open via file:// inside a sandboxed iframe.

Design tokens (in :root, keep the names — re-theme by changing values only)

--paper:        #FBFAF8;                    /* cream paper, every page */
--panel:        #FFFFFF;                    /* data-card surface */
--ink:          #232036;                    /* deep ink text */
--ink-70:       rgba(35, 32, 54, 0.72);     /* prose body */
--ink-45:       rgba(35, 32, 54, 0.46);     /* captions, chrome */
--hairline:     rgba(35, 32, 54, 0.12);     /* all rules */
--accent:       #635BFF;                    /* Stripe purple — the ONLY accent */
--accent-soft:  rgba(99, 91, 255, 0.08);    /* tint panels, quote marks */
--serif:        "Newsreader", "Source Serif 4", "Noto Serif SC", Georgia, serif;
--serif-text:   "Source Serif 4", "Newsreader", "Noto Serif SC", Georgia, serif;
--sans:         "Inter", "Noto Sans SC", -apple-system, sans-serif;

• Fonts via Google Fonts @import: Newsreader (display, incl. italic), Source Serif 4 (prose), Noto Serif SC (CJK serif), Inter, Noto Sans SC.
• All numerals tabular: the shared .num class sets font-variant-numeric: tabular-nums; every metric, year, and display number uses it.
• One accent. Never a second hue, never a gradient, never a dark slide.

Letter chrome (every page)

• Letterhead top strip with hairline rule: publication/company name left (small-caps Inter, letter-spaced, brand word in accent), issue + date right.
• Footer hairline rule: section name left, author/issue meta right. Page numbering lives only in the runtime counter pill — never also printed inside a slide.
• Headings in var(--serif) (Newsreader/Noto Serif SC), weight 500–600 — letters are set elegantly, not boldly; key words get class="hl" (accent), never the whole heading.
• Kicker: small-caps Inter label with a short 44×3px accent bar above section titles.
• Chinese copy uses 「」 quotes; 中英混排 keeps English in Newsreader italic.

Signature devices (the genre — use them, don't substitute)

…